A088782 - OEIS

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A088782

a(n) = smallest k>0 such that concatenation of n^k and 1 is prime, or 0 if no such number exists.

1, 2, 1, 1, 2, 1, 1, 2, 2, 1, 10, 0, 1, 6, 1, 3, 1356, 1, 1, 2, 1, 15, 0, 1, 1, 2, 1, 1, 4, 2, 1, 0, 1, 0, 2, 3, 2, 4, 4, 1, 2, 1, 1, 6, 0, 1, 2, 2, 1, 4, 3, 1, 16, 1, 9, 0, 1, 2, 36, 1, 165, 66, 1, 1, 0, 1, 0, 6, 1, 1, 2, 12, 3, 138, 1, 1, 4, 0, 5, 4, 1, 1, 2, 5, 2, 2, 3, 1, 0, 2, 1, 24, 2, 1, 42, 7, 1, 0, 1

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OFFSET

1,2

COMMENTS

a(185) > 10^6, see link. Richard N. Smith, Jul 16 2019

LINKS

Richard N. Smith, Table of n, a(n) for n = 1..184

Karsten Bonath, Proth prime small bases least n

Richard N. Smith, Table of n, a(n) for n = 1..500 status

MATHEMATICA

f[n_] := Block[{k = 1}, While[ !PrimeQ[10*n^k + 1], k++ ]; k]]; f[1] = 1; Table[ f[n], {n, 1, 99}] (* Robert G. Wilson v, Oct 29 2003 *)

PROG