Let G be a finite group and π（G） = {pl,p2,…… ,pk} be the set of the primes dividing the order of G. We define its prime graph F（G） as follows. The vertex set of this graph is 7r（G）, and two distinct vertices ...Let G be a finite group and π（G） = {pl,p2,…… ,pk} be the set of the primes dividing the order of G. We define its prime graph F（G） as follows. The vertex set of this graph is 7r（G）, and two distinct vertices p, q are joined by an edge if and only if pq ∈ πe（G）. In this case, we write p - q. For p ∈π（G）, put deg（p） ：= ｜{q ∈ π（G）｜p - q}｜, which is called the degree of p. We also define D（G） ：= （deg（p1）, deg（p2）,..., deg（pk））, where pl 〈 p2 〈 -……〈 pk, which is called the degree pattern of G. We say a group G is k-fold OD-characterizable if there exist exactly k non-isomorphic finite groups with the same order and degree pattern as G. Specially, a l-fold OD-characterizable group is simply called an OD-characterizable group. Let L ：= U6（2）. In this article, we classify all finite groups with the same order and degree pattern as an almost simple groups related to L. In fact, we prove that L and L.2 are OD-characterizable, L.3 is 3-fold OD-characterizable, and L.S3 is 5-fold OD-characterizable.展开更多
The degree pattern of a finite group has been introduced in [18]. A group M is called k-fold OD- characterizable if there exist exactly k non-isomorphic finite groups having the same order and degree pattern as M. In ...The degree pattern of a finite group has been introduced in [18]. A group M is called k-fold OD- characterizable if there exist exactly k non-isomorphic finite groups having the same order and degree pattern as M. In particular, a 1-fold OD-characterizable group is simply called OD-characterizable. It is shown that the alternating groups Am and Am＋l, for m = 27, 35, 51, 57, 65, 77, 87, 93 and 95, are OD-characterizable, while their automorphism groups are 3-fold OD-characterizable. It is also shown that the symmetric groups Sin＋2, for m=7, 13, 19, 23, 31, 37, 43, 47, 53, 61, 67, 73, 79, 83, 89 and 97, are 3-fold OD-characterizable. From this, the following theorem is derived. Let m be a natural number such that m≤100. Then one of the following holds： （a） if m ≠10, then the alternating groups Am are OD-characterizable, while the symmetric groups Sm are ODcharacterizable or 3-fold OD-characterizable; （b） the alternating group A10 is 2-fold OD-characterizable; （c） the symmetric group S10 is 8-fold OD-characterizable. This theorem completes the study of OD-characterizability of the alternating and symmetric groups Am and Sm of degree m≤100.展开更多
The degree pattern of a finite group G associated with its prime graph has been introduced by Moghaddamfar in 2005 and it is proved that the following simple groups are uniquely determined by their order and degree pa...The degree pattern of a finite group G associated with its prime graph has been introduced by Moghaddamfar in 2005 and it is proved that the following simple groups are uniquely determined by their order and degree patterns： All sporadic simple groups, the alternating groups Ap （p ≤ 5 is a twin prime） and some simple groups of the Lie type. In this paper, the authors continue this investigation. In particular, the authors show that the symmetric groups Sp＋3, where p ＋ 2 is a composite number and p ＋ 4 is a prime and 97 〈 p ∈π（1000!）, are 3-fold OD-characterizable. The authors also show that the alternating groups All6 and A134 are OD-characterizable. It is worth mentioning that the latter not only generalizes the results by Hoseini in 2010 but also gives a positive answer to a conjecture by Moghaddamfar in 2009.展开更多
The prime graph of a finite group G, which is denoted by GK（G）, is a simple graph whose vertex set is comprised of the prime divisors of ｜G｜ and two distinct prime divisors p and q are joined by an edge if and onl...The prime graph of a finite group G, which is denoted by GK（G）, is a simple graph whose vertex set is comprised of the prime divisors of ｜G｜ and two distinct prime divisors p and q are joined by an edge if and only if there exists an element of order pq in G. Let P1 〈 P2 〈 … 〈 Pk be all prime divisors of ｜G｜- Then the degree pattern of G is defined as D（G） = （degG（pl）, degG（p2）,..., degG（pk））, where degG（p） signifies the degree of the vertex p in GK（G）. A finite group H is said to be OD-characterizable if G ≌ H for every finite group G such that ｜G｜ = ｜H｜and D（G） = D（H）. The purpose of this article is threefold. First, it finds sharp upper and lower bounds on v（G）, the sum of degrees of all vertices in GK（G）, for any finite group G （Theorem 2.1）. Second, it provides the degree of vertices 2 and the characteristic p of the base field of any finite simple group of Lie type in their prime graphs （Propositions 3.1-3.7）. Third, it proves the linear groups L4（q）, q = 19, 23, 27, 29, 31, 32, and 37, are OD-characterizable （Theorem 4.2）.展开更多
Let G be a finite group with order ｜G｜=p1^α1p2^α2……pk^αk, where p1 〈 p2 〈……〈 Pk are prime numbers. One of the well-known simple graphs associated with G is the prime graph （or Gruenberg- Kegel graph） den...Let G be a finite group with order ｜G｜=p1^α1p2^α2……pk^αk, where p1 〈 p2 〈……〈 Pk are prime numbers. One of the well-known simple graphs associated with G is the prime graph （or Gruenberg- Kegel graph） denoted .by г（G） （or GK（G））. This graph is constructed as follows： The vertex set of it is π（G） = {p1,p2,…,pk} and two vertices pi, pj with i≠j are adjacent by an edge （and we write pi - pj） if and only if G contains an element of order pipj. The degree deg（pi） of a vertex pj ∈π（G） is the number of edges incident on pi. We define D（G） ：= （deg（p1）, deg（p2）,..., deg（pk））, which is called the degree pattern of G. A group G is called k-fold OD-characterizable if there exist exactly k non- isomorphic groups H such that ｜H｜ = ｜G｜ and D（H） = D（G）. Moreover, a 1-fold OD-characterizable group is simply called OD-characterizable. Let L ：= U3（5） be the projective special unitary group. In this paper, we classify groups with the same order and degree pattern as an almost simple group related to L. In fact, we obtain that L and L.2 are OD-characterizable; L.3 is 3-fold OD-characterizable; L.S3 is 6-fold OD-characterizable.展开更多
For G a finite group,π_e(G)denotes the set of orders of elements in G.If Ω is a subset of the set of natural numbers,h(Ω)stands for the number of isomorphism classes of finite groups with the same set Ω of element...For G a finite group,π_e(G)denotes the set of orders of elements in G.If Ω is a subset of the set of natural numbers,h(Ω)stands for the number of isomorphism classes of finite groups with the same set Ω of element orders.We say that G is k-distinguishable if h(π_(G))=k<∞,otherwise G is called non-distinguishable.Usually,a 1-distinguishable group is called a characterizable group.It is shown that if M is a sporadic simple group different from M_(12),M_(22),J_2,He,Suz,M^cL and O'N, then Aut(M)is charaeterizable by its dement orders.It is also proved that if M is isomorphic to M_(12),M_(22),He,Suz or O'N,then h(π_e(Aut(M)))∈{1,∞}.展开更多
The spectrum of a finite group is the set of its element orders,and two groups are said to be isospectral if they have the same spectra.A finite group G is said to be recognizable by spectrum,if every finite group iso...The spectrum of a finite group is the set of its element orders,and two groups are said to be isospectral if they have the same spectra.A finite group G is said to be recognizable by spectrum,if every finite group isospectral with G is isomorphic to G.We prove that if S is one of the sporadic simple groups M^(c)L,M_(12),M_(22),He,Suz and O'N,then Aut(S)is recognizable by spectrum.This finishes the proof of the recognizability by spectrum of the automorphism groups of all sporadic simple groups,except J_(2).展开更多
In this paper, We show that the simple K\-3-groups can be characterized by the orders of their maximal abelian subgroups. That is, we have Theorem Let G be a finite group and M a simple K \-3-group. Then ...In this paper, We show that the simple K\-3-groups can be characterized by the orders of their maximal abelian subgroups. That is, we have Theorem Let G be a finite group and M a simple K \-3-group. Then G is isomorphic to M if and only if the set of the orders of the maximal abelian subgoups of G is the same as that of M .展开更多
In this paper,it is proved that all the alternating groups A_(p+5) are ODcharacterizable and the symmetric groups S_(p+5) are 3-fold OD-characterizable,where p + 4 is a composite number and p + 6 is a prime and 5≠p∈...In this paper,it is proved that all the alternating groups A_(p+5) are ODcharacterizable and the symmetric groups S_(p+5) are 3-fold OD-characterizable,where p + 4 is a composite number and p + 6 is a prime and 5≠p∈π(1000!).展开更多
For a finite group G, it is denoted by N（G） the set of conjugacy class sizes of G. In 1980s, J. G. Thompson posed the following conjecture： if L is a finite nonabelian simple group, G is a finite group with trivial...For a finite group G, it is denoted by N（G） the set of conjugacy class sizes of G. In 1980s, J. G. Thompson posed the following conjecture： if L is a finite nonabelian simple group, G is a finite group with trivial center, and N（G） = N（L）, then L and G are isomorphic. In this paper, it is proved that Thompson＇s conjecture is true for the alternating group A22 with connected prime graph.展开更多
基金supported by Natural Science Foundation Project of CQ CSTC (2010BB9206)NNSF of China (10871032)+1 种基金Fundamental Research Funds for the Central Universities (Chongqing University, CDJZR10100009)National Science Foundation for Distinguished Young Scholars of China (11001226)
文摘Let G be a finite group and π（G） = {pl,p2,…… ,pk} be the set of the primes dividing the order of G. We define its prime graph F（G） as follows. The vertex set of this graph is 7r（G）, and two distinct vertices p, q are joined by an edge if and only if pq ∈ πe（G）. In this case, we write p - q. For p ∈π（G）, put deg（p） ：= ｜{q ∈ π（G）｜p - q}｜, which is called the degree of p. We also define D（G） ：= （deg（p1）, deg（p2）,..., deg（pk））, where pl 〈 p2 〈 -……〈 pk, which is called the degree pattern of G. We say a group G is k-fold OD-characterizable if there exist exactly k non-isomorphic finite groups with the same order and degree pattern as G. Specially, a l-fold OD-characterizable group is simply called an OD-characterizable group. Let L ：= U6（2）. In this article, we classify all finite groups with the same order and degree pattern as an almost simple groups related to L. In fact, we prove that L and L.2 are OD-characterizable, L.3 is 3-fold OD-characterizable, and L.S3 is 5-fold OD-characterizable.
基金partially supported by a research grant fromthe Institute for Research in Fundamental Sciences (IPM)
文摘The degree pattern of a finite group has been introduced in [18]. A group M is called k-fold OD- characterizable if there exist exactly k non-isomorphic finite groups having the same order and degree pattern as M. In particular, a 1-fold OD-characterizable group is simply called OD-characterizable. It is shown that the alternating groups Am and Am＋l, for m = 27, 35, 51, 57, 65, 77, 87, 93 and 95, are OD-characterizable, while their automorphism groups are 3-fold OD-characterizable. It is also shown that the symmetric groups Sin＋2, for m=7, 13, 19, 23, 31, 37, 43, 47, 53, 61, 67, 73, 79, 83, 89 and 97, are 3-fold OD-characterizable. From this, the following theorem is derived. Let m be a natural number such that m≤100. Then one of the following holds： （a） if m ≠10, then the alternating groups Am are OD-characterizable, while the symmetric groups Sm are ODcharacterizable or 3-fold OD-characterizable; （b） the alternating group A10 is 2-fold OD-characterizable; （c） the symmetric group S10 is 8-fold OD-characterizable. This theorem completes the study of OD-characterizability of the alternating and symmetric groups Am and Sm of degree m≤100.
基金the National Natural Science Foundation of China(Nos.11271301,11171364)the National Science Foundation for Distinguished Young Scholars of China(No.11001226)+2 种基金the Fundamental Research Funds for the Central Universities(Nos.XDJK2012D004,XDJK2009C074)the Natural Science Foundation Project of CQ CSTC(Nos.2011jjA00020,2010BB9206)the GraduateInnovation Funds of Science of Southwest University(No.ky2009013)
文摘The degree pattern of a finite group G associated with its prime graph has been introduced by Moghaddamfar in 2005 and it is proved that the following simple groups are uniquely determined by their order and degree patterns： All sporadic simple groups, the alternating groups Ap （p ≤ 5 is a twin prime） and some simple groups of the Lie type. In this paper, the authors continue this investigation. In particular, the authors show that the symmetric groups Sp＋3, where p ＋ 2 is a composite number and p ＋ 4 is a prime and 97 〈 p ∈π（1000!）, are 3-fold OD-characterizable. The authors also show that the alternating groups All6 and A134 are OD-characterizable. It is worth mentioning that the latter not only generalizes the results by Hoseini in 2010 but also gives a positive answer to a conjecture by Moghaddamfar in 2009.
文摘The prime graph of a finite group G, which is denoted by GK（G）, is a simple graph whose vertex set is comprised of the prime divisors of ｜G｜ and two distinct prime divisors p and q are joined by an edge if and only if there exists an element of order pq in G. Let P1 〈 P2 〈 … 〈 Pk be all prime divisors of ｜G｜- Then the degree pattern of G is defined as D（G） = （degG（pl）, degG（p2）,..., degG（pk））, where degG（p） signifies the degree of the vertex p in GK（G）. A finite group H is said to be OD-characterizable if G ≌ H for every finite group G such that ｜G｜ = ｜H｜and D（G） = D（H）. The purpose of this article is threefold. First, it finds sharp upper and lower bounds on v（G）, the sum of degrees of all vertices in GK（G）, for any finite group G （Theorem 2.1）. Second, it provides the degree of vertices 2 and the characteristic p of the base field of any finite simple group of Lie type in their prime graphs （Propositions 3.1-3.7）. Third, it proves the linear groups L4（q）, q = 19, 23, 27, 29, 31, 32, and 37, are OD-characterizable （Theorem 4.2）.
基金Supported by National Natural Science Foundation of China (Grant No. 10871032)the SRFDP of China (Grant No. 20660285002)a subproject of National Natural Science Foundation of China (Grant No. 50674008) (Chongqing University, Nos. 104207520080834, 104207520080968)
文摘Let G be a finite group with order ｜G｜=p1^α1p2^α2……pk^αk, where p1 〈 p2 〈……〈 Pk are prime numbers. One of the well-known simple graphs associated with G is the prime graph （or Gruenberg- Kegel graph） denoted .by г（G） （or GK（G））. This graph is constructed as follows： The vertex set of it is π（G） = {p1,p2,…,pk} and two vertices pi, pj with i≠j are adjacent by an edge （and we write pi - pj） if and only if G contains an element of order pipj. The degree deg（pi） of a vertex pj ∈π（G） is the number of edges incident on pi. We define D（G） ：= （deg（p1）, deg（p2）,..., deg（pk））, which is called the degree pattern of G. A group G is called k-fold OD-characterizable if there exist exactly k non- isomorphic groups H such that ｜H｜ = ｜G｜ and D（H） = D（G）. Moreover, a 1-fold OD-characterizable group is simply called OD-characterizable. Let L ：= U3（5） be the projective special unitary group. In this paper, we classify groups with the same order and degree pattern as an almost simple group related to L. In fact, we obtain that L and L.2 are OD-characterizable; L.3 is 3-fold OD-characterizable; L.S3 is 6-fold OD-characterizable.
基金This work has been partially sopported by the Research Institute for Fundamental Sciences Tabriz,Iran
文摘For G a finite group,π_e(G)denotes the set of orders of elements in G.If Ω is a subset of the set of natural numbers,h(Ω)stands for the number of isomorphism classes of finite groups with the same set Ω of element orders.We say that G is k-distinguishable if h(π_(G))=k<∞,otherwise G is called non-distinguishable.Usually,a 1-distinguishable group is called a characterizable group.It is shown that if M is a sporadic simple group different from M_(12),M_(22),J_2,He,Suz,M^cL and O'N, then Aut(M)is charaeterizable by its dement orders.It is also proved that if M is isomorphic to M_(12),M_(22),He,Suz or O'N,then h(π_e(Aut(M)))∈{1,∞}.
基金This work is supported by Russian Science Foundation(Project No.14-21-00065).
文摘The spectrum of a finite group is the set of its element orders,and two groups are said to be isospectral if they have the same spectra.A finite group G is said to be recognizable by spectrum,if every finite group isospectral with G is isomorphic to G.We prove that if S is one of the sporadic simple groups M^(c)L,M_(12),M_(22),He,Suz and O'N,then Aut(S)is recognizable by spectrum.This finishes the proof of the recognizability by spectrum of the automorphism groups of all sporadic simple groups,except J_(2).
文摘In this paper, We show that the simple K\-3-groups can be characterized by the orders of their maximal abelian subgroups. That is, we have Theorem Let G be a finite group and M a simple K \-3-group. Then G is isomorphic to M if and only if the set of the orders of the maximal abelian subgoups of G is the same as that of M .
基金supported by the National Natural Science Foundation of China(Nos.11171364,11271301,11471266,11426182)the Fundamental Research Funds for the Central Universities(Nos.XDJK2014C163,XDJK2014C162)+2 种基金the Natural Science Foundation Project of CQ CSTC(No.cstc2014jcyj A00010)the Postdoctoral Science Foundation of Chongqing(No.Xm2014029)the China Postdoctoral Science Foundation(No.2014M562264)
文摘In this paper,it is proved that all the alternating groups A_(p+5) are ODcharacterizable and the symmetric groups S_(p+5) are 3-fold OD-characterizable,where p + 4 is a composite number and p + 6 is a prime and 5≠p∈π(1000!).
基金Project supported by the NNSF of China(No.10571128)the SRFDP of China(No.20060285002)Young Teachers Fund of College of Mathematics and Physics,Chongqing University(2005)
文摘For a finite group G, it is denoted by N（G） the set of conjugacy class sizes of G. In 1980s, J. G. Thompson posed the following conjecture： if L is a finite nonabelian simple group, G is a finite group with trivial center, and N（G） = N（L）, then L and G are isomorphic. In this paper, it is proved that Thompson＇s conjecture is true for the alternating group A22 with connected prime graph.
