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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 2,1
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EXAMPLE
| 2^2*(2^2-1)-1=11 prime so a(2)=2.
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MATHEMATICA
| f[n_] := Block[{k = 1, c}, While[c = n^k; ! PrimeQ[c*(c - 1) - 1], k++ ]; Return[k]; ]; Table[f[n], {n, 2, 72}] (*Chandler*)
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CROSSREFS
| Cf. A101406.
Sequence in context: A115413 A069283 A033630 * A062760 A014649 A070084
Adjacent sequences: A101443 A101444 A101445 * A101447 A101448 A101449
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KEYWORD
| nonn,more
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AUTHOR
| Pierre CAMI (pierre-cami(AT)bbox.fr), Jan 24 2005
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EXTENSIONS
| a(55)-a(72) from Ray Chandler (rayjchandler(AT)sbcglobal.net), Jan 27 2005
a(73)>2475. - Ray Chandler (rayjchandler(AT)sbcglobal.net), Jan 27 2005
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