A087699 Greater twin prime p such that 2^p-1 is composite.

43, 73, 103, 109, 139, 151, 181, 193, 199, 229, 241, 271, 283, 313, 349, 421, 433, 463, 523, 571, 601, 619, 643, 661, 811, 823, 829, 859, 883, 1021, 1033, 1051, 1063, 1093, 1153, 1231, 1291, 1303, 1321, 1429, 1453, 1483, 1489, 1609, 1621, 1669, 1699, 1723

Offset

0,1

Comments

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

Links

Harvey P. Dale, Table of n, a(n) for n = 0..420

Mathematica

Transpose[Select[Partition[Prime[Range[300]], 2, 1], Last[#]-First[#] == 2&&!PrimeQ[2^Last[#]-1]&]][[2]] (* Harvey P. Dale, Oct 20 2013 *)

Prog

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

Crossrefs

Sequence in context: A141971 A144974 A144975 * A054807 A285017 A139932

Adjacent sequences: A087696 A087697 A087698 * A087700 A087701 A087702

Keyword

easy,nonn

Author

Cino Hilliard, Oct 25 2003

Extensions

Corrected and extended by Ray Chandler, Nov 07 2003

Status

approved