OFFSET
1,2
PROG
(PARI) f(n) = sumdiv(n, d, n % (sum(m=0, n-1, Mod(m, n)^d == m)/sum(m=0, n-1, -Mod(m, n)^d == m)) == 0); \\ A337454
isok(n) = f(n) == numdiv(n);
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Marcus, Oct 15 2020
STATUS
approved