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arXiv 2106.14217math.GRmath.CO
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关于幂图是余图的有限群

On finite groups whose power graph is a cograph

Peter J. Cameron, Pallabi Manna, Ranjit Mehatari

摘要:

无$P_4$的图称为余图。本文部分刻画了幂图是余图的有限群。正如我们将看到的,这个问题是群的决定的一个推广,其中每个元素都有素数幂阶,这个问题首先由Graham Higman在1957年提出,最近得到了充分的解决。首先我们确定所有的群$G$和$H$,其中$G\times H$的幂图是余图。我们表明,集团的权力图是一个cograph可以其特征在于一个条件,只涉及元素的订单是素数或产品的两个(可能相等)素数。一些重要的图形类也被考虑在内。对于有限单群,我们证明了在大多数情况下它们的幂图不是上图:只有某些群PSL $(2,q)$和Sz $(q)$以及群PSL $(3,4)$的幂图是上图。然而,这些群的完全确定涉及到一些困难的数论问题。

英文摘要:

A $P_4$-free graph is called a cograph. In this paper we partially characterize finite groups whose power graph is a cograph. As we will see, this problem is a generalization of the determination of groups in which every element has prime power order, first raised by Graham Higman in 1957 and fully solved very recently. First we determine all groups $G$ and $H$ for which the power graph of $G\times H$ is a cograph. We show that groups whose power graph is a cograph can be characterised by a condition only involving elements whose orders are prime or the product of two (possibly equal) primes. Some important graph classes are also taken under consideration. For finite simple groups we show that in most of the cases their power graphs are not cographs: the only ones for which the power graphs are cographs are certain groups PSL$(2,q)$ and Sz$(q)$ and the group PSL$(3,4)$. However, a complete determination of these groups involves some hard number-theoretic problems.

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