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Finite groups with conjugacy classes number one greater than its same order classes number

Xianglin Du·Wujie Shi
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Abstract

Let $k(G)$ be the number of conjugacy classes of finite groups $G$ and $π_e(G)$ be the set of the orders of elements in $G$. Then there exists a non-negative integer $k$ such that $k(G)=|π_e(G)|+k$. We call such groups to be $co(k)$ groups. This paper classifies all finite $co(1)$ groups. They are isomorphic to one of the following groups: $A_5, L_2(7), S_5, Z_3, Z_4, S_4, A_4$, $D_{10}, Hol(Z_5)$, or $Z_3\rtimes Z_4$.

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Xianglin Du, Wujie Shi. 2005-09-16. Finite groups with conjugacy classes number one greater than its same order classes number. https://arxiv.org/abs/math/0509376

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