OFFSET
1,2
PROG
(PARI) f(n) = my(v=select(x->gcd(x, n)==1, [1..n-1])); vecsum(apply(x->(x*lift(1/Mod(x, n))-1)/n, v)); \\ A074639
isok(k) = (f(k) % eulerphi(k)) == 0; \\ Michel Marcus, Jul 05 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Michele Dondi (bik.mido(AT)tiscalinet.it), Sep 18 2002
EXTENSIONS
More terms from Michel Marcus, Jul 05 2021
STATUS
approved