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

1,1

Comments

A118255(1314) is prime with 396 digits

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

Links

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

Example

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

Mathematica

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

Crossrefs

Cf. A005171, A118255, A118256.

Sequence in context: A358428 A084909 A038619 * A378029 A066762 A066198

Adjacent sequences: A118254 A118255 A118256 * A118258 A118259 A118260

Keyword

nonn,more

Author

Pierre CAMI, Apr 19 2006

Extensions

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

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

Status

approved