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A098814 a(n) is the least k such that k*Mersenne_prime(n) - 1 and k*Mersenne_prime(n) + 1 are twin primes. 1
2, 6, 42, 144, 72, 312, 144, 234, 1512, 672, 2226, 1104, 34632, 267894, 371634, 909030, 384750, 3198240, 2445810, 1639494 (list; graph; refs; listen; history; text; internal format)
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 A156437

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

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Last modified October 16 05:41 EDT 2021. Contains 348035 sequences. (Running on oeis4.)