A098915 Least k such that k*Mersenne-prime(n)*Mersenne-prime(n+1) - 1 is prime.

2, 2, 2, 24, 2, 50, 6, 26, 14, 306, 86, 846, 104, 1832, 272, 2222, 2540, 884, 5474, 1950, 28358, 13338, 76740

Offset

1,1

Links

Table of n, a(n) for n=1..23.

Example

2*(2^2-1)*(2^3-1) - 1 = 41 is prime, so a(1) = 2.
2*(2^3-1)*(2^5-1) - 1 = 433 is prime, so a(2) = 2.

Mathematica

f[n_] := Module[{k = 1}, While[!PrimeQ[k*n - 1], k++]; k]; f /@ Times @@@ Partition[2^MersennePrimeExponent[Range[15]] - 1, 2, 1] (* Amiram Eldar, Jul 24 2021 *)

Crossrefs

Cf. A000043, A000668.

Sequence in context: A067097 A260082 A153438 * A095855 A157979 A147975

Adjacent sequences: A098912 A098913 A098914 * A098916 A098917 A098918

Keyword

nonn,more

Author

Pierre CAMI, Oct 17 2004

Extensions

a(15)-a(23) from Amiram Eldar, Jul 24 2021

Status

approved