OFFSET
1,1
COMMENTS
An odd prime p is in the sequence iff p is not in A004061.
PROG
(PARI) isokd(n) = (n>5) && !isprime(n) && (gcd(n, 5)==1) && (znorder(Mod(5, n)) * (sumdiv(n, d, eulerphi(d)/znorder(Mod(5, d))) - 1) + 1 == n); \\ A141390
isok(n) = {fordiv (5^n-1, dd, if (isokd(dd), return (1)); ); return (0); } \\ Michel Marcus, Oct 25 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Shevelev, Jun 30 2008
EXTENSIONS
Corrected and more terms from Michel Marcus, Oct 25 2018
STATUS
approved