A104038 a(n) is the least k such that k*(k+1)*Mersenne-prime(n)+1 is prime.

1, 2, 3, 12, 8, 3, 5, 14, 17, 69, 189, 42, 392, 167, 377, 12, 2007, 434, 744, 705, 1089, 1109, 7833, 7328, 1271, 192, 6770, 2379

Offset

1,2

Links

Table of n, a(n) for n=1..28.

Example

1*2*(2^2-1)+1 = 7 is prime, so a(1) = 1.
2*3*(2^3-1)+1 = 43 is prime, so a(2) = 2.
3*4*(2^5-1)+1 = 373 is prime, so a(3) = 3.

Mathematica

f[p_] := Module[{k = 1}, While[! PrimeQ[k*(k + 1)*p + 1], k++]; k]; f /@ (2^MersennePrimeExponent[Range[15]] - 1) (* Amiram Eldar, Jul 18 2021 *)

Crossrefs

Cf. A000043, A000668.

Sequence in context: A282075 A282514 A320810 * A112979 A225723 A092972

Adjacent sequences: A104035 A104036 A104037 * A104039 A104040 A104041

Keyword

nonn,more

Author

Pierre CAMI, Mar 31 2005

Extensions

a(14) inserted and a(24)-a(28) added by Amiram Eldar, Jul 18 2021

Status

approved