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5, 76, 1065, 14840, 206701, 2878980, 40099025, 558507376, 7779004245, 108347552060, 1509086724601, 21018866592360, 292755045568445, 4077551771365876, 56792969753553825, 791024024778387680, 11017543377143873701, 153454583255235844140, 2137346622196157944265
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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COMMENTS
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Also integers n such that n^2+(n+1)^2 is equal to the sum of two consecutive octagonal numbers. - Colin Barker, Dec 20 2014
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REFERENCES
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Mario Velucchi, "Seeing couples", Recreational and Educational Computing, to appear 1997. [apparently never materialized, Joerg Arndt, Aug 14 2013]
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LINKS
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FORMULA
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a(n) = +15*a(n-1) -15*a(n-2) +a(n-3). G.f.: -x*(5+x)/ ((x-1) * (x^2-14*x+1)). - R. J. Mathar, Apr 15 2010
a(n) = (-6-(7-4*sqrt(3))^n*(-3+sqrt(3))+(3+sqrt(3))*(7+4*sqrt(3))^n)/12. - Colin Barker, Mar 05 2016
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MATHEMATICA
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CoefficientList[Series[-(5 + x) / ((x - 1) (x^2 - 14 x + 1)), {x, 0, 30}], x] (* Vincenzo Librandi, Aug 13 2013 *)
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PROG
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(PARI) Vec(-x*(5+x)/((x-1)*(x^2-14*x+1)) + O(x^100)) \\ Colin Barker, Dec 20 2014
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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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Mario Velucchi (mathchess(AT)velucchi.it)
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EXTENSIONS
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STATUS
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approved
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