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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 (list; graph; refs; listen; history; text; internal format)
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: A094016 A116033 A290469 * 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

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Last modified October 19 08:33 EDT 2021. Contains 348074 sequences. (Running on oeis4.)