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Search: id:A067872
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| A067872 |
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Least m>0 for which m*n^2 + 1 is a square. |
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+0
4
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| 3, 2, 7, 3, 23, 8, 47, 15, 79, 24, 119, 2, 167, 48, 3, 63, 287, 80, 359, 6, 88, 120, 527, 28, 623, 168, 727, 12, 839, 44, 959, 255, 216, 288, 8, 20, 1367, 360, 19, 77, 1679, 22, 1847, 30, 208, 528, 2207, 7, 2399, 624, 128, 42, 2807, 728, 696, 3, 160, 840, 3479, 11
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Least m>0 for which x^2 - m*y^2 = 1 has a solution with y = n.
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..500
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FORMULA
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For n a power of an odd prime, a(n)=n^2-2. For n twice a power of an odd prime, a(n)=(n/2)^2-1. - T. D. Noe, Sep 13 2007
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EXAMPLE
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a(4)=3, based on 3*4^2 + 1 = 7^2.
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MATHEMATICA
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a[n_] := For[m=1, True, m++, If[IntegerQ[Sqrt[m*n^2+1]], Return[m]]]
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CROSSREFS
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Cf. A033318, A068310.
Sequence in context: A057020 A165794 A075270 this_sequence A011772 A060451 A129187
Adjacent sequences: A067869 A067870 A067871 this_sequence A067873 A067874 A067875
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KEYWORD
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nice,nonn
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AUTHOR
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Lekraj Beedassy (blekraj(AT)yahoo.com), Feb 25 2002
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EXTENSIONS
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Edited by Dean Hickerson (dean.hickerson(AT)yahoo.com), Mar 19 2002
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