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A263942
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Positive integers n such that (n+4)^3 - n^3 is a square.
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9
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6, 28, 110, 416, 1558, 5820, 21726, 81088, 302630, 1129436, 4215118, 15731040, 58709046, 219105148, 817711550, 3051741056, 11389252678, 42505269660, 158631825966, 592022034208, 2209456310870, 8245803209276, 30773756526238, 114849222895680, 428623135056486
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OFFSET
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1,1
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LINKS
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FORMULA
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a(n) = 5*a(n-1)-5*a(n-2)+a(n-3) for n>3.
G.f.: 2*x*(x-3) / ((x-1)*(x^2-4*x+1)).
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EXAMPLE
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6 is in the sequence because (6+4)^3 - 6^3 = 28^2.
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MATHEMATICA
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LinearRecurrence[{5, -5, 1}, {6, 28, 110}, 30] (* Paolo Xausa, Mar 04 2024 *)
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PROG
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(PARI) Vec(2*x*(x-3)/((x-1)*(x^2-4*x+1)) + O(x^40))
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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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