OFFSET
1,1
COMMENTS
If m is a squarefree semiprime, then A324331(m) is a square. But the converse is not always true.
LINKS
B. Alspach, Research problems, Problem 18, Discrete Math 40 (1982), page 126.
EXAMPLE
A324331(45) = 64, a square, even though 45 is not squarefree semiprime, so 45 is a term.
PROG
(PARI) f(n) = (n-1)^2 - eulerphi(n)*sigma(n); \\ A324331
isok(n) = !((bigomega(n) == 2) && issquarefree(n)) && issquare(f(n));
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Marcus, Feb 23 2019
STATUS
approved