A124516 a(n) = least k such that 2^i*k-1 is prime for 1<=i<=n.

2, 2, 3, 3, 45, 45, 561330, 9549960, 42932385, 13044904290, 277344139215, 277344139215, 2045466215756535

Offset: 1

Author

Artur Jasinski, Nov 04 2006

Keywords

• nonn
• more

Crossrefs

Cf. A006254, A124485, A124493, A124494, A124017, A125113, A124514, A124515.

Cf. A071576, A101994, A101320.

Programs

Mathematica

k = 1; Do[If[n < 5, inc = 1, inc = 15];If[Mod[k, inc] > 0, k = k + inc - Mod[k, inc]];While[Nand @@ PrimeQ[Table[2^j, {j, n}]*k - 1], k += inc]; Print[k], {n, 1, 10}] (* Ray Chandler *)

Extensions

Definition corrected and a(10) calculated by Farideh Firoozbakht, Nov 24 2006

a(11)-a(13) from Giovanni Resta, Apr 22 2019