A121172 Smallest integer k>0 such that k*10^n + 1 is a prime.

1, 1, 3, 7, 7, 22, 3, 6, 6, 3, 19, 18, 4, 39, 6, 13, 37, 15, 15, 6, 16, 9, 96, 61, 19, 6, 9, 3, 33, 63, 57, 117, 55, 49, 30, 3, 28, 6, 42, 24, 36, 72, 21, 60, 6, 24, 33, 61, 21, 85, 31, 49, 13, 93, 18, 90, 9, 16, 135, 19, 55, 9, 135, 60, 6, 30, 3, 16, 115, 114, 19, 99, 15, 147, 171, 42

Offset: 1

Author

Alexander Adamchuk, Aug 14 2006

Keywords

• nonn

Examples

			a(1) = 1 because A030430[1] = 11 is a smallest prime of form 10*k + 1.
a(2) = 1 because A062800[1] = 101 is a smallest prime of form 100*k + 1.
		

Links

• Robert Price, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A030430, A062800, see A070854 for resulting primes.

Programs

Mathematica

s={};Do[k=0;Until[PrimeQ[k*10^n+1],k++];AppendTo[s,k],{n,76}];s (* James C. McMahon, Oct 13 2024 *)

Formula

a(n) = (A070854(n)-1)/10^n. - Ray Chandler, Feb 10 2009

Extensions

Minor edits by Ray Chandler, Feb 10 2009