A120642 Smallest integer k>0 such that k*10^n - 1 is a prime.

2, 2, 2, 5, 2, 3, 2, 8, 11, 6, 11, 35, 6, 5, 15, 14, 11, 21, 3, 21, 14, 6, 6, 80, 8, 2, 2, 6, 9, 48, 48, 21, 15, 6, 44, 11, 9, 15, 18, 6, 33, 30, 3, 278, 74, 92, 89, 33, 8, 71, 59, 11, 2, 5, 3, 24, 108, 47, 39, 41, 6, 14, 53, 173, 26, 26, 51, 114, 23, 17, 246, 44, 6, 131, 56, 8, 26, 77, 74

Offset

1,1

Links

Pierre CAMI, Table of n,a(n) for n=1,...,3000

Example

The primes are 19, 199, 1999, 49999, 199999, 2999999,
19999999, 799999999, 10999999999, 59999999999, ...,.

Mathematica

f[n_] := Block[{k = 1}, While[ !PrimeQ[k*10^n - 1], k++ ]; k]; Array[f, 79] (* Robert G. Wilson v *)

Crossrefs

Cf. A030430, A037071, A062800, A065582, A121172.

Sequence in context: A350403 A113516 A226525 * A216624 A183413 A183380

Adjacent sequences: A120639 A120640 A120641 * A120643 A120644 A120645

Keyword

easy,nonn

Author

Jonathan Vos Post, Aug 17 2006

Extensions

a(11) onwards from Robert G. Wilson v, Aug 20 2006

Status

approved