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A084746
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Smallest k such that n^k - k is a prime, or 0 if no such number exists.
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3
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2, 1, 1, 2, 1, 2, 1, 2, 3, 18, 1, 2, 1, 2, 3, 6, 1, 2, 1, 2, 41, 110, 1, 18, 3, 2, 11, 2, 1, 24, 1, 2, 3, 2
(list; graph; refs; listen; history; internal format)
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OFFSET
| 2,1
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COMMENTS
| Conjecture: no entry is zero.
If n is odd, k=a(n) is even. If n is even, k=a(n) is odd. n and k=a(n) are coprime. - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Apr 02 2006
a(36)>30000 or 0. a(37)..a(46) = 2, 1, 8, 3, 24, 1, 2, 1, 514, 6737.
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MAPLE
| a := proc(n) local k; k := 1; while not isprime(n^k-k) do k := k+1 od; k end: seq(a(n), n=2..35);
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MATHEMATICA
| f[n_] := Block[{k = 1}, If[OddQ[n], k++ ]; While[ ! PrimeQ[n^k - k], k += 2]; k]; Table[ f[n], {n, 3, 35}]
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CROSSREFS
| Cf. A084745.
Sequence in context: A053574 A065203 A029396 * A128259 A051194 A134838
Adjacent sequences: A084743 A084744 A084745 * A084747 A084748 A084749
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KEYWORD
| more,nonn
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AUTHOR
| Amarnath Murthy and Meenakshi Srikanth (amarnath_murthy(AT)yahoo.com), Jun 15 2003
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EXTENSIONS
| Edited and extended by Robert G. Wilson v (rgwv(AT)rgwv.com), Alec Mihailovs (Alec(AT)Mihailovs.com) and T. D. Noe (noe(AT)sspectra.com), Jun 16 2003.
Update on a(36) and a(46) from Max Alekseyev (maxale(AT)gmail.com), Apr 24 2009
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