A098814 a(n) is the least k such that k*Mersenne_prime(n) - 1 and k*Mersenne_prime(n) + 1 are twin primes.

2, 6, 42, 144, 72, 312, 144, 234, 1512, 672, 2226, 1104, 34632, 267894, 371634, 909030, 384750, 3198240, 2445810, 1639494

Offset

1,1

Links

Table of n, a(n) for n=1..20.

Example

a(1) = 2 since A000668(1) = 3, and 2*3-1 = 5 and 2*3+1 = 7 are twin primes.

Mathematica

f[p_] := Module[{k = 1}, While[!PrimeQ[k*p - 1] || !PrimeQ[k*p + 1], k++]; k]; f /@ (2^MersennePrimeExponent[Range[10]]-1) (* Amiram Eldar, Jul 18 2021 *)

Crossrefs

Cf. A000043, A000668, A001097.

Sequence in context: A033936 A203618 A334883 * A272177 A346548 A321250

Adjacent sequences: A098811 A098812 A098813 * A098815 A098816 A098817

Keyword

nonn,more

Author

Pierre CAMI, Oct 07 2004

Extensions

a(16)-a(20) from Amiram Eldar, Jul 18 2021

Status

approved