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 A101180 Numbers n such that 19*n^2 + 19*n + 1 is a square. 3
 0, 8, 671, 15639, 42159, 981911, 77624048, 1807894920, 4873553880, 113507005568, 8973184757831, 208989037004319, 563373081435879, 13121182828725551, 1037282211558181688, 24158714697817430640, 65124801462951244560, 1516782492521509296728 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Define a(1)=0, a(2)=8, a(3)=671, a(4)=15639, a(5)=42159, a(6)=981911, the first 6 terms found for the sequence then a(7)=57799*(2*a(3)+1)-a(2)-1, a(8)=57799*(2*a(4)+1)-a(1)-1 for n>8 a(n)=57799*(2*a(n-4)+1)-a(n-8)-1 remark:57799 = 38*39*39+1 =2*19*(39^2)+1 LINKS Index entries for linear recurrences with constant coefficients, signature (1,0,0,115598,-115598,0,0,-1,1). FORMULA G.f.: -x^2*(8*x^6+663*x^5+14968*x^4+26520*x^3+14968*x^2+663*x+8) / ((x-1)*(x^4-340*x^2+1)*(x^4+340*x^2+1)). - Colin Barker, Mar 05 2013 CROSSREFS Cf. A105839. Sequence in context: A099126 A172919 A286394 * A128875 A199801 A278857 Adjacent sequences: A101177 A101178 A101179 * A101181 A101182 A101183 KEYWORD nonn,easy AUTHOR Pierre CAMI, Apr 06 2005, Apr 22 2005 EXTENSIONS Edited by N. J. A. Sloane, Aug 29 2008 at the suggestion of R. J. Mathar More terms (using recursive formula in comment) from Jon E. Schoenfield, Jul 10 2010 a(18) from Colin Barker, Mar 05 2013 STATUS approved

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Last modified February 1 08:20 EST 2023. Contains 359992 sequences. (Running on oeis4.)