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Search: id:A015580
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| A015580 |
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Linear 2nd order recurrence. |
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+0
1
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| 0, 1, 9, 85, 801, 7549, 71145, 670501, 6319089, 59553805, 561260601, 5289560629, 49851088065, 469818035101, 4427766668169, 41729172153925, 393273616058001, 3706379233137709, 34930507562471385
(list; graph; listen)
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OFFSET
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0,3
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FORMULA
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a(n) = 9 a(n-1) + 4 a(n-2).
G.f.:1/(1-9*x-4*x^2) . [From Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Dec 20 2008]
a(n)=(1/97)*sqrt(97)*{[(9/2)+(1/2)*sqrt(97)]^n-[(9/2)-(1/2)*sqrt(97)]^n}, with n>=0 [From Paolo P. Lava (ppl(AT)spl.at), Jan 13 2009]
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PROGRAM
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(Other) sage: [lucas_number1(n, 9, -4) for n in xrange(0, 19)]# [From Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Apr 26 2009]
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CROSSREFS
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Sequence in context: A086627 A024118 A166902 this_sequence A163308 A160112 A108427
Adjacent sequences: A015577 A015578 A015579 this_sequence A015581 A015582 A015583
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KEYWORD
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nonn,easy
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AUTHOR
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Olivier Gerard (olivier.gerard(AT)gmail.com)
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