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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. 3
 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 (list; graph; refs; listen; history; text; internal format)
 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 (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)))) \\ Richard N. Smith, Jul 16 2019 CROSSREFS Cf. A088622, A088783. Sequence in context: A205154 A025898 A025849 * A291984 A066672 A134024 Adjacent sequences:  A088779 A088780 A088781 * A088783 A088784 A088785 KEYWORD base,nonn AUTHOR Ray Chandler, Oct 23 2003 STATUS approved

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Last modified March 29 19:35 EDT 2020. Contains 333117 sequences. (Running on oeis4.)