A118257 Numbers k such that A118255(k) is prime.

2, 6, 8, 10, 18, 26, 30, 74, 142, 203, 398, 651, 792, 1314, 3487, 5978, 6240, 7814, 8054, 8673, 21436, 23947, 52985, 91784, 157537, 164901

Offset: 1

Author

Pierre CAMI, Apr 19 2006

Keywords

• nonn
• more

Comments

A118255(1314) is prime with 396 digits

A118255(23947) is a probable prime with 7209 digits. - Giovanni Resta, Apr 26 2006

Examples

			A118255(2) = 2 prime, A118255(6) = 149 prime, A118255(8) = 599 prime.
		

Crossrefs

Cf. A005171, A118255, A118256.

Programs

Mathematica

A118255[n_] := Module[{},
   If[n == 1, A118255[1] = 1,
    If[PrimeQ[n], A118255[n] = 2 A118255[n - 1],
     A118255[n] = 2 A118255[n - 1] + 1]]];
Select[Range[5000], PrimeQ[A118255[#]] &] (* Robert Price, Apr 03 2019 *)

Extensions

a(15)-a(22) from Giovanni Resta, Apr 26 2006

a(23)-a(26) from Michael S. Branicky, Dec 11 2024