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A088782
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a(n) = smallest k>0 such that concatenation of n^k and 1 is prime, or 0 if no such number exists.
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3
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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
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1,2
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COMMENTS
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a(185) > 10^6, see link. Richard N. Smith, Jul 16 2019
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LINKS
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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
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MATHEMATICA
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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 *)
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PROG
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(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
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CROSSREFS
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Cf. A088622, A088783.
Sequence in context: A337772 A025898 A025849 * A291984 A066672 A134024
Adjacent sequences: A088779 A088780 A088781 * A088783 A088784 A088785
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KEYWORD
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base,nonn
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AUTHOR
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Ray Chandler, Oct 23 2003
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STATUS
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approved
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