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

1,1

Comments

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

Links

Table of n, a(n) for n=1..69.

Prog

(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); }

Crossrefs

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

Sequence in context: A116033 A290469 A375320 * A297255 A296699 A297132

Adjacent sequences: A140504 A140505 A140506 * A140508 A140509 A140510

Keyword

nonn

Author

Vladimir Shevelev, Jun 30 2008

Extensions

More terms from Michel Marcus, Oct 25 2018

Status

approved