A087858 Lesser of twin primes p such that 2^p-1 is prime.

3, 5, 17, 107, 521

Offset

1,1

Comments

If there are any further terms, they will be no smaller than 56220127 as the GIMPS project has tested and verified all exponents below 56220127. - David R. Kirkby, Jul 19 2021

Links

Table of n, a(n) for n=1..5.

GIMPS, GIMPS Great Internet Mersenne Prime Search

Mathematica

twinPrimeAboveQ[n_]:=PrimeQ[n+2]
Table[MersennePrimeExponent[n], {n, 47}] // Select[twinPrimeAboveQ]
(* David R. Kirkby, Jul 19 2021 *)

Prog

(PARI) twopm1(n) = { sr=0; forprime(x=2, n, y=2^x-1; if(isprime(x+2), y2=2^(x+2)-1, y2=0); if(isprime(y) && isprime(x+2), print1(x", "); sr+=1.0/y; sr+=1.0/y2; ) ); }

Crossrefs

Cf. A000043, A297674.

Sequence in context: A346791 A174722 A176131 * A191222 A084723 A288376

Adjacent sequences: A087855 A087856 A087857 * A087859 A087860 A087861

Keyword

nonn,hard,more

Author

Cino Hilliard, Oct 25 2003

Status

approved