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731, 2920, 6567, 11672, 18235, 26256, 35735, 46672, 59067, 72920, 88231, 105000, 123227, 142912, 164055, 186656, 210715, 236232, 263207, 291640, 321531, 352880, 385687, 419952, 455675, 492856, 531495, 571592, 613147, 656160, 700631, 746560
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OFFSET
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1,1
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COMMENTS
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The identity (729*n+1)^2-(729*n^2+2*n)*(27)^2=1 can be written as A158397(n)^2-a(n)*(27)^2=1.
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LINKS
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FORMULA
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a(n) = 3*a(n-1) -3*a(n-2) +a(n-3).
G.f.: x*(731+727*x)/(1-x)^3.
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MATHEMATICA
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LinearRecurrence[{3, -3, 1}, {731, 2920, 6567}, 50]
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PROG
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(Magma) I:=[731, 2920, 6567]; [n le 3 select I[n] else 3*Self(n-1)-3*Self(n-2)+1*Self(n-3): n in [1..50]];
(PARI) a(n) = 729*n^2 + 2*n.
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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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