Groups of prime-fifth order

This article is about the groups of prime-fifth order, i.e., order $p^{5}$ where $p$ is an odd prime. The cases $p=2$ (see groups of order 32) and $p=3$ (see groups of order 243) are somewhat different from the general case $p\geq 5$.

$p^{5}$ is the smallest prime power for which the number of groups of that order is not eventually constant, but rather, is given by a nonconstant PORC function in keeping with Higman's PORC conjecture.

Statistics at a glance

Quantity	Value case $p=2$	Value case $p=3$	PORC function for $p\geq 5$
Total number of groups	51	67	$2p+61+2\operatorname {gcd} (p-1,3)+\operatorname {gcd} (p-1,4)$
Number of abelian groups	7	7	7
Number of groups of nilpotency class exactly two	26	28	$p+25$
Number of groups of nilpotency class exactly three	15	26	$p+26$
Number of groups of nilpotency class exactly four (maximal class groups)	3	6	$3+2\operatorname {gcd} (p-1,3)+\operatorname {gcd} (p-1,4)$