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A076942
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Smallest k > 0 such that nk+1 is a square.
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5
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3, 4, 1, 2, 3, 4, 5, 1, 7, 8, 9, 2, 11, 12, 1, 3, 15, 16, 17, 4, 3, 20, 21, 1, 23, 24, 25, 6, 27, 4, 29, 7, 3, 32, 1, 8, 35, 36, 5, 2, 39, 4, 41, 10, 8, 44, 45, 1, 47, 48, 5, 12, 51, 52, 8, 3, 7, 56, 57, 2, 59, 60, 1, 15, 3, 8, 65, 16, 7, 12, 69, 4, 71, 72, 9, 18, 15, 8, 77, 1, 79, 80, 81
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| a(n) <= n-2 for n > 2; a(p) = p-2 if p is a prime > 2. [Comment corrected by Floris van Doorn, Jan 31 2009]
a(n) = n - 2 precisely when n > 2 has a primitive root; that is, for 4, and p^k and 2*p^k for p an odd prime and k > 0. [From Franklin T. Adams-Watters (FrankTAW(AT)Netscape.net), Apr 13 2009]
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LINKS
| Floris P. van Doorn, Table of n=2C a(n) for n=0...10000
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MATHEMATICA
| Do[k = 1; While[ !IntegerQ[Sqrt[n*k + 1]], k++ ]; Print[k], {n, 1, 85}]
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CROSSREFS
| Cf. A033948, A033949. [From Franklin T. Adams-Watters (FrankTAW(AT)Netscape.net), Apr 13 2009]
Sequence in context: A204999 A085710 A106650 * A205127 A021971 A171073
Adjacent sequences: A076939 A076940 A076941 * A076943 A076944 A076945
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KEYWORD
| nonn
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AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Oct 19 2002
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EXTENSIONS
| Edited and extended by Robert G. Wilson v (rgwv(AT)rgwv.com), Oct 21 2002
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