A098556 Least k such that k*Mersenne - prime(n) + 1 is prime.

2, 4, 10, 4, 46, 12, 16, 46, 52, 136, 166, 114, 336, 154, 1474, 156, 1086, 1816, 2010, 9436, 1746, 3426, 6238, 40138, 858, 4018, 17262, 15418

Offset: 1

Author

Pierre CAMI, Sep 14 2004

Keywords

• hard
• nonn

Crossrefs

Cf. A000043, A000668, A098555.

Programs

Mathematica

mexp = {the list in A000043}; f[n_] := Block[{k = 2, mp = 2^mexp[[n]] - 1}, While[ !PrimeQ[mp*k + 1] && k < 10000, k += 2 ]; If[k == 10000, 0, k]]; Do[ Print[ f[n]], {n, 21}] (* Robert G. Wilson v, Sep 17 2004 *)

Extensions

a(21)=1746 corrected, other terms verified, a(23)-a(28) extended by Ray Chandler, Apr 16 2009