A161676 Isolated primes p such that 2^p-1 is also a prime number.

2, 89, 127, 607, 2203, 2281, 3217, 4253, 9689, 9941, 11213, 19937, 21701, 23209, 44497, 86243, 216091, 756839, 859433, 1257787, 1398269, 2976221, 3021377, 6972593, 13466917

Offset

1,1

Links

Table of n, a(n) for n=1..25.

Formula

A000043 INTERSECT A007510.

Example

For the isolated prime p=2= A007510(1), p^2-1=3 is prime, which adds p=2 to the sequence.

Maple

MP := [2, 3, 5, 7, 13, 17, 19, 31, 61, 89, 107, 127, 521, 607, 1279, 2203, 2281, 3217, 4253, 4423, 9689, 9941, 11213, 19937, 21701, 23209, 44497, 86243, 110503, 132049, 216091, 756839, 859433, 1257787, 1398269, 2976221, 3021377, 6972593, 13466917]:
n := 0: for j to 39 do if `and`(isprime(MP[j]-2) = false, isprime(MP[j]+2) = false) then n := n+1; a[n] := MP[j] else end if end do:
seq(a[n], n = 1 .. 25); # Emeric Deutsch, Jun 20 2009

Crossrefs

Cf. A000043, A007510.

Sequence in context: A355272 A105268 A139881 * A235467 A249305 A023302

Adjacent sequences: A161673 A161674 A161675 * A161677 A161678 A161679

Keyword

nonn

Author

Vladislav-Stepan Malakhovsky & Juri-Stepan Gerasimov, Jun 16 2009

Extensions

More terms from Emeric Deutsch, Jun 20 2009

Definition rephrased by R. J. Mathar, Sep 23 2009

Status

approved