A171255 Primes which are the average of two distinct Mersenne primes (A000668).

5, 17, 19, 67, 79, 4099, 4111, 4159, 65537, 65539, 65551, 65599, 262147, 266239, 1073741827, 1073741839, 1073807359, 309485009821345068724785151

Offset

1,1

Comments

The subsequence of primes in A171253, which equals A171254 minus its subsequence A000668.

Links

Table of n, a(n) for n=1..18.

Jonathan Vos Post, Sums of three Mersenne primes, and prime sums of three Mersenne primes, SeqFan list, Mar 5, 2010.

Formula

A171255 = A171253 intersect A000040 = A171254 \ A000668.

Example

a(n) = A171253(n) for n=1,2,3, since all of these terms are prime. The term A171253(4) = 65 is the first element of A171252 to be composite, and therefore not included in the present sequence A171255.

Prog

(PARI) select(isprime, concat(vector(#A00668, i, vector(i-1, j, A00668[i]+A00668[j])))/2) /* having defined A00668 as vector with initial terms of A000668. In PARI version 2.4.2, the syntax select( concat(...), x->isprime(x)) must be used. */

Crossrefs

Cf. A171252, A171254 (includes elements of A000668).

Sequence in context: A153320 A171253 A226623 * A304540 A306125 A255901

Adjacent sequences: A171252 A171253 A171254 * A171256 A171257 A171258

Keyword

nonn,changed

Author

M. F. Hasler, Mar 06 2010

Status

approved