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A140452 2^(a(n))-1 contains an overpseudoprime divisor. 1
11, 22, 23, 25, 28, 29, 33, 35, 36, 37, 39, 41, 43, 44, 45, 46, 47, 48, 50, 51, 52, 53, 55, 56, 57, 58, 59, 60, 63, 64, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 81, 82, 83, 84, 86, 87, 88, 90, 91, 92, 94, 95, 96, 97, 99, 100, 101, 102, 103, 104, 105, 106, 108, 109 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

If p is a prime then p is in the sequence iff 2^p-1 is a composite number.

LINKS

Table of n, a(n) for n=1..68.

V. Shevelev, Overpseudoprimes, Mersenne Numbers and Wieferich Primes, arXiv:0806.3412 [math.NT], 2008-2012.

PROG

(PARI) f(n) = my(t); sumdiv(2*n+1, d, eulerphi(d)/(t=znorder(Mod(2, d))))*t-t+1; \\ A137576

isopp(n) = (n>1) && !isprime(n) && (n == f((n-1)/2)); \\ A141232

isok(n) = {fordiv(2^n-1, d, if (isopp(d), return (1)); ); return (0); } \\ Michel Marcus, Dec 09 2018

CROSSREFS

Cf. A141232, A137576, A005420, A049479.

Sequence in context: A139337 A231115 A040110 * A048136 A180054 A166713

Adjacent sequences:  A140449 A140450 A140451 * A140453 A140454 A140455

KEYWORD

nonn

AUTHOR

Vladimir Shevelev, Jun 26 2008

EXTENSIONS

More terms from Michel Marcus, Dec 09 2018

STATUS

approved

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Last modified January 21 15:00 EST 2019. Contains 319350 sequences. (Running on oeis4.)