A135978 Primes p such that 2^p-1 has exactly 2 prime factors.

11, 23, 37, 41, 59, 67, 83, 97, 101, 103, 109, 131, 137, 139, 149, 167, 197, 199, 227, 241, 269, 271, 281, 293, 347, 373, 379, 421, 457, 487, 523, 727, 809, 881, 971, 983, 997, 1061, 1063

Offset

1,1

Comments

a(40)>=1277. - Amiram Eldar, Sep 29 2018

Links

Table of n, a(n) for n=1..39.

Mathematica

k = {}; Do[If[ ! PrimeQ[2^Prime[n] - 1], c = FactorInteger[2^Prime[n] - 1]; d = Length[c]; If[d == 2, AppendTo[k, Prime[n]]]], {n, 1, 40}]; k

Crossrefs

Cf. A000225, A065341, A054723, A134852, A135975, A135976, A135977.

Sequence in context: A101859 A079664 A160268 * A280915 A139493 A275591

Adjacent sequences: A135975 A135976 A135977 * A135979 A135980 A135981

Keyword

nonn,more

Author

Artur Jasinski, Dec 09 2007

Extensions

a(17)-a(37) from Arkadiusz Wesolowski, Jan 26 2012

a(38)-a(39) from Amiram Eldar, Sep 29 2018

Status

approved