A087693 Lesser twin prime p such that 2^p-1 is composite.

11, 29, 41, 59, 71, 101, 137, 149, 179, 191, 197, 227, 239, 269, 281, 311, 347, 419, 431, 461, 569, 599, 617, 641, 659, 809, 821, 827, 857, 881, 1019, 1031, 1049, 1061, 1091, 1151, 1229, 1277, 1289, 1301, 1319, 1427, 1451, 1481, 1487, 1607, 1619, 1667, 1697

Offset

0,1

Comments

Look at all twin primes (p1, p2); if 2^p1 - 1 is composite print p2.

Links

Table of n, a(n) for n=0..48.

Prog

(PARI) twopm1(n) = { forprime(x=2, n, y=2^x-1; if(!isprime(y) && isprime(x+2), print1(x", ") ) ) }

Crossrefs

Sequence in context: A353043 A350420 A240678 * A106017 A343418 A106065

Adjacent sequences: A087690 A087691 A087692 * A087694 A087695 A087696

Keyword

easy,nonn

Author

Cino Hilliard, Oct 25 2003

Extensions

More terms from Ray Chandler, Nov 07 2003

Status

approved