A098819 Least k such that k*(Mersenne_prime(n)^2) + 1 is prime.

2, 4, 16, 12, 22, 28, 30, 22, 138, 12, 102, 180, 426, 1444, 9502, 6568, 2212, 5380, 9942, 3034, 24222, 31530, 2962, 7848, 93280, 3718

Offset

1,1

Comments

Subsequence of A035092. - Amiram Eldar, Mar 01 2019

Links

Table of n, a(n) for n=1..26.

Example

2*((2^2-1)^2)+1=19 prime so a(1)=2.

Mathematica

a[n_] := Module[{k = 1, m = (2^MersennePrimeExponent[n] - 1)^2}, While[! PrimeQ[k*m + 1], k++]; k]; Array[a, 20] (* Amiram Eldar, Mar 01 2019 *)

Crossrefs

Cf. A000043, A000668, A035092.

Sequence in context: A186110 A073923 A153666 * A186008 A067846 A155893

Adjacent sequences: A098816 A098817 A098818 * A098820 A098821 A098822

Keyword

more,nonn

Author

Pierre CAMI, Oct 08 2004

Extensions

a(19)-a(22) from Donovan Johnson, Mar 23 2008

a(23)-a(26) from Amiram Eldar, Mar 01 2019

Status

approved