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Numbers n such that A118255(n) is prime.
5

%I #14 Apr 04 2019 03:00:46

%S 2,6,8,10,18,26,30,74,142,203,398,651,792,1314,3487,5978,6240,7814,

%T 8054,8673,21436,23947

%N Numbers n such that A118255(n) is prime.

%C A118255(1314) is prime with 396 digits

%C A118255(23947) is a probable prime with 7209 digits. - _Giovanni Resta_, Apr 26 2006

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

%t A118255[n_] := Module[{},

%t If[n == 1, A118255[1] = 1,

%t If[PrimeQ[n], A118255[n] = 2 A118255[n - 1],

%t A118255[n] = 2 A118255[n - 1] + 1]]];

%t Select[Range[5000], PrimeQ[A118255[#]] &] (* _Robert Price_, Apr 03 2019 *)

%Y Cf. A005171, A118255, A118256.

%K nonn,more

%O 1,1

%A _Pierre CAMI_, Apr 19 2006

%E a(15)-a(22) from _Giovanni Resta_, Apr 26 2006