A088782 a(n) is the 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

Offset

1,2

Comments

a(185) > 10^6, see link. - Eric Chen, Jul 16 2019

Links

Eric Chen, Table of n, a(n) for n = 1..184

Karsten Bonath, Proth prime small bases least n

Eric Chen, 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, 11}] (* Robert G. Wilson v, Oct 29 2003 *)

Prog

(PARI) a(n)=if((n%11==1 || n%33==32) && n>1, 0, for(k=1, 10^6, if(ispseudoprime(10*n^k+1), return(k)))) \\ Eric Chen, Jul 16 2019

Crossrefs

Cf. A088622, A088783.

Sequence in context: A378284 A025898 A025849 * A291984 A066672 A134024

Adjacent sequences: A088779 A088780 A088781 * A088783 A088784 A088785

Keyword

base,nonn

Author

Ray Chandler, Oct 23 2003

Status

approved