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A154376
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a(n) = 25*n^2 - 2*n.
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4
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23, 96, 219, 392, 615, 888, 1211, 1584, 2007, 2480, 3003, 3576, 4199, 4872, 5595, 6368, 7191, 8064, 8987, 9960, 10983, 12056, 13179, 14352, 15575, 16848, 18171, 19544, 20967, 22440, 23963, 25536, 27159, 28832, 30555, 32328, 34151, 36024
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OFFSET
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1,1
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COMMENTS
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The identity (1250*n^2 - 100*n + 1)^2 - (25*n^2 - 2*n)*(250*n - 10)^2 = 1 can be written as A154374(n)^2 - a(n)*A154378(n)^2 = 1 (see also the second comment in A154374). - Vincenzo Librandi, Jan 30 2012
The continued fraction expansion of sqrt(a(n)) is [5n-1; {1, 3, 1, 10n-2}]. - Magus K. Chu, Sep 04 2022
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LINKS
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FORMULA
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G.f.: x*(23 + 27*x)/(1-x)^3.
a(n) = 3*a(n-1) -3*a(n-2) +a(n-3). (End)
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MATHEMATICA
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PROG
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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