# Open problems concerning all the finite groups

What are the open problems concerning all the finite groups?

The references will be appreciated. Here are two examples:

• Aschbacher-Guralnick conjecture (AG1984 p.447): the number of conjugacy classes of maximal subgroups of a finite group is at most its class number (i.e. the number of conjugacy classes of elements, or the number of irreducible complex representations up to equiv.).

• K.S. Brown's problem (B2000 Q.4; SW2016 p.760): Let $$G$$ be a finite group, $$\mu$$ be the Möbius function of its subgroup lattice $$L(G)$$. Then the sum $$\sum_{H \in L(G)}\mu(H,G)|G:H|$$ is nonzero.

There are two types of problems, those involving an upper/lower bound (like Aschbacher-Guralnick conjecture) and those "exact", involving no bound (like K.S. Brown's problem). I guess the first type is much more abundant than the second, so for the first type, please restrict to the main problems.

• It's not clear what's a theorem/problem about "all" finite groups. A theorem about nilpotent finite groups, for instance, can provide information to Sylow subgroups of all finite groups, etc. Many problems about "all" finite groups are treated by reduction to special subcases (e.g., simple groups). – YCor Mar 24 at 13:04
• I would suggest not to restrict to "all" finite group - just finite groups would be ok, imho. It does not seems to me that we get so many answers that it would be difficult to navigate, and subdivision to "all" - "not all" would be justified – Alexander Chervov Mar 24 at 17:09
• I like this open problem (mathoverflow.net/q/316434/61536) on prime factrization of finite groups: Can each finite group $G$ be written as the product $G=A_1\cdots A_n$ of subsets of prime cardinality such that $|G|=|A_1|\cdots|A_n|$? – Taras Banakh Mar 24 at 17:22

• (4.55) Let $$G$$ be a finite group and $$\mathbb{Z}_p$$ the localization at $$p$$. Does the Krull-Schmidt theorem hold for projective $$\mathbb{Z}_pG$$-modules?
• (8.51) If $$G$$ is a finite group and $$p$$ a prime, let $$m_p(G)$$ denote the number of ordinary irreducible characters of $$G$$ whose degree is not divisible by $$p$$. Let $$P$$ be a Sylow $$p$$-subgroup of $$G$$. Is it true that $$m_p(G) = m_p(N_G(P))$$?
The questions I picked are all of the form "Is $$P$$ true for all finite groups $$G$$?". There are many questions of the form "Characterize the finite groups $$G$$ for which $$P$$ holds", which to my ears has a slightly different ring to it than what you were asking for. There are also some questions regarding the class of finite groups, which again is a different interpretation.