A102629 - OEIS

A102629

a(n) is the least k such that (10^k)*Mersenne-prime(n) + 1 is prime.

1, 1, 1, 4, 2, 3, 10, 6, 28, 12, 45, 23, 36, 18, 114, 72, 652, 47, 39, 61, 3713, 208, 9655, 965, 11508, 684, 7085, 1803

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OFFSET

1,4

COMMENTS

Primes certified using PFGW from Primeform group.

LINKS

EXAMPLE

(10^1)*(2^5-1) + 1 = 10*31 + 1 = 311 is prime, 2^5-1 = Mersenne-prime(3) so a(3) = 1.

MATHEMATICA

f[n_] := Module[{k = 1}, While[! PrimeQ[10^k*n + 1], k++]; k]; f /@ (2^MersennePrimeExponent[Range[15]]-1) (* Amiram Eldar, Jul 18 2021 *)

CROSSREFS

KEYWORD

nonn,more

AUTHOR

Pierre CAMI, Feb 01 2005

EXTENSIONS

a(23)-a(28) from Amiram Eldar, Jul 18 2021

STATUS

approved