A177464 The smallest positive k such that the n-th Mersenne prime +-k are two primes.

4, 12, 24, 30, 30, 66, 954, 1920, 30, 4116, 576, 214608

Offset

2,1

Comments

Smallest k>0 such that A000668(n)+k and A000668(n)-k are both prime.

Links

Table of n, a(n) for n=2..13.

Formula

a(n) = A082467(A000668(n)). - R. J. Mathar, Jan 23 2011

Example

7+-4->primes, 31+-12->primes, 127+-24->primes, 8191+-30->primes, 131071+-30->primes, 524287+-66->primes..

Mathematica

g[n_]:=2^Prime[n]-1; f[n_]:=Block[{k}, If[OddQ[n], k=2, k=1]; While[ !PrimeQ[n-k]||!PrimeQ[n+k], k+=2]; k]; lst={}; Do[If[PrimeQ[g[n]], AppendTo[lst, f[g[n]]]], {n, 2, 40}]; lst

Crossrefs

Cf. A000668, A082467.

Sequence in context: A353991 A286040 A332608 * A316985 A353789 A273315

Adjacent sequences: A177461 A177462 A177463 * A177465 A177466 A177467

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, May 09 2010

Status

approved