A089319 Smallest k > 1 such that k^n followed by digit 1 is a prime.

3, 2, 3, 3, 6, 2, 3, 6, 3, 11, 7, 2, 70, 2, 22, 18, 43, 3, 4, 649, 15, 3, 37, 2, 24, 13, 4, 8, 40, 77, 19, 22, 13, 24, 292, 48, 4, 2, 109, 792, 30, 4, 18, 5, 7, 90, 28, 138, 132, 891, 9, 25, 145, 2, 24, 9, 40, 28, 219, 165, 40, 41, 4, 13, 261, 24, 6, 30, 6, 154, 82, 22, 120, 2, 55

Offset

1,1

Links

Michael S. Branicky, Table of n, a(n) for n = 1..1000

Example

a(4) = 3 as concatenation of 3^4 and 1 = 811 is a prime. 161 is not a prime.

Mathematica

Do[k = 2; While[ !PrimeQ[10*k^n + 1], k++ ]; Print[k], {n, 1, 30}] (* Ryan Propper, Jul 08 2005 *)

Prog

(PARI) a(n) = my(k=2); while (!isprime(10*k^n+1), k++); k; \\ Michel Marcus, Mar 07 2025

Crossrefs

Cf. A089318.

Sequence in context: A058680 A070544 A087713 * A140396 A117231 A106151

Adjacent sequences: A089316 A089317 A089318 * A089320 A089321 A089322

Keyword

base,nonn

Author

Amarnath Murthy, Nov 03 2003

Extensions

Corrected and extended by Ryan Propper, Jul 08 2005

Further terms from David Wasserman, Sep 09 2005

Status

approved