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A015532
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a(n) = 4 a(n-1) + 7 a(n-2).
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10
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0, 1, 4, 23, 120, 641, 3404, 18103, 96240, 511681, 2720404, 14463383, 76896360, 408829121, 2173591004, 11556167863, 61439808480, 326652408961, 1736688295204, 9233320043543, 49090098240600, 260993633267201
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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FORMULA
| O.g.f.: -x/(-1+4*x+7*x^2). a(n)=-7^n*(A^n-B^n)/(2sqrt(11)) where A=-1/(2+sqrt(11)) and B=1/(sqrt(11)-2) . - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Apr 29 2008
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MATHEMATICA
| a[n_]:=(MatrixPower[{{1, 2}, {1, -5}}, n].{{1}, {1}})[[2, 1]]; Table[Abs[a[n]], {n, -1, 40}] [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Feb 19 2010]
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PROG
| (Other) sage: [lucas_number1(n, 4, -7) for n in xrange(0, 21)]# [From Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Apr 23 2009]
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CROSSREFS
| Sequence in context: A124507 A174248 A201350 * A144465 A024050 A193808
Adjacent sequences: A015529 A015530 A015531 * A015533 A015534 A015535
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KEYWORD
| nonn,easy
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AUTHOR
| Olivier Gerard (olivier.gerard(AT)gmail.com)
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