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A101446
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a(n)= least k such that n^k*(n^k-1)-1 is prime with n > 1.
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1
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2, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 10, 1, 5, 1, 1, 2, 2, 1, 1, 1, 2, 4, 1, 4, 1, 12, 1, 328, 1, 1, 6, 24, 77, 1, 8, 75, 1, 1, 2, 1, 2, 13, 1, 1, 1, 14, 1, 3, 1, 45, 3, 1, 1, 1, 1, 8, 625, 1, 1, 22, 3, 3, 1, 1, 1, 11, 1, 4, 1, 2
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OFFSET
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2,1
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COMMENTS
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LINKS
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EXAMPLE
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2^2*(2^2-1)-1=11 prime so a(2)=2.
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MATHEMATICA
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f[n_] := Block[{k = 1, c}, While[c = n^k; ! PrimeQ[c*(c - 1) - 1], k++ ]; Return[k]; ]; Table[f[n], {n, 2, 72}] (* Ray Chandler, Jan 27 2005 *)
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PROG
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(PARI) a(n) = {my(k=1); while (!ispseudoprime(n^k*(n^k-1)-1), k++); k; } \\ Michel Marcus, Sep 16 2019
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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