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A140507
Numbers k such that 3^k-1 contains a divisor which is an overpseudoprime in base 3.
0
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.
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
KEYWORD
nonn
AUTHOR
Vladimir Shevelev, Jun 30 2008
EXTENSIONS
More terms from Michel Marcus, Oct 25 2018
STATUS
approved