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A118257 Numbers n such that A118255(n) is prime. 5
2, 6, 8, 10, 18, 26, 30, 74, 142, 203, 398, 651, 792, 1314, 3487, 5978, 6240, 7814, 8054, 8673, 21436, 23947 (list; graph; refs; listen; history; text; internal format)
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..22.

EXAMPLE

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

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 *)

CROSSREFS

Cf. A005171, A118255, A118256.

Sequence in context: A324175 A084909 A038619 * A066762 A066198 A299381

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

STATUS

approved

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Last modified February 26 17:04 EST 2021. Contains 341632 sequences. (Running on oeis4.)