A140507 Numbers k such that 3^k-1 contains a divisor which is an overpseudoprime in base 3.

5, 10, 11, 15, 16, 17, 18, 19, 20, 22, 23, 25, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 64, 65, 66, 67, 68, 69, 70, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85

Offset: 1

Author

Vladimir Shevelev, Jun 30 2008

Keywords

• nonn

Comments

An odd prime p is in the sequence iff p is not in A028491.

Crossrefs

Cf. A141350, A020229, A141232, A141390, A003462, A028491.

Programs

PARI

isokd(n) = (n!=1) && !isprime(n) && (gcd(n,3)==1) && (znorder(Mod(3,n)) * (sumdiv(n, d, eulerphi(d)/znorder(Mod(3, d))) - 1) + 1 == n); \\ A141350
isok(n) = {fordiv (3^n-1, d, if (isokd(d), return (1));); return (0);}

Extensions

More terms from Michel Marcus, Oct 25 2018