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Search: id:A154262
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| 3, 2, 19, 54, 107, 178, 267, 374, 499, 642, 803, 982, 1179, 1394, 1627, 1878, 2147, 2434, 2739, 3062, 3403, 3762, 4139, 4534, 4947, 5378, 5827, 6294, 6779, 7282, 7803, 8342, 8899, 9474, 10067, 10678, 11307, 11954, 12619, 13302, 14003, 14722, 15459
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OFFSET
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1,1
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COMMENT
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Pell's equation X^2+AY^2=1, with A=a(n), X=9*a(n)-1, Y^2=81*a(n)-18. ex: a(n)= A=2; X=17, Y=12, then 17^2-2*12^2=1 9*a(n)-2 is a square. ex: a(n)=54, 9*54-2=22^2
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FORMULA
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a(n)=9n^2-10n+3
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EXAMPLE
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For n=0, a(0)=3, n=1, a(1)=2; n=4, a(4)=107.
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CROSSREFS
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Cf. A154261, A154254
Sequence in context: A066195 A090587 A094554 this_sequence A154261 A098655 A065038
Adjacent sequences: A154259 A154260 A154261 this_sequence A154263 A154264 A154265
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KEYWORD
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nonn
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AUTHOR
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Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Jan 06 2009
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