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

Offset

1,4

Comments

Primes certified using PFGW from Primeform group.

Links

Table of n, a(n) for n=1..28.

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

Cf. A000043, A000668.

Sequence in context: A120240 A179394 A347265 * A082361 A082363 A026177

Adjacent sequences: A102626 A102627 A102628 * A102630 A102631 A102632

Keyword

nonn,more

Author

Pierre CAMI, Feb 01 2005

Extensions

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

Status

approved