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A189734
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a(1)=2, a(2)=5, a(n)=2*a(n-1) + 5*a(n-2).
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13
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2, 5, 20, 65, 230, 785, 2720, 9365, 32330, 111485, 384620, 1326665, 4576430, 15786185, 54454520, 187839965, 647952530, 2235104885, 7709972420, 26595469265, 91740800630, 316458947585, 1091621898320, 3765538534565, 12989186560730, 44806065794285
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OFFSET
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1,1
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LINKS
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Vincenzo Librandi, Table of n, a(n) for n = 1..100
Index entries for linear recurrences with constant coefficients, signature (2, 5).
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FORMULA
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a(n) = (1-sqrt(6))^(n-1)+(1+sqrt(6))^(n-1)+1/4*sqrt(6)*((1+sqrt(6))^(n-1)-(1-sqrt(6))^(n-1)). - Paolo P. Lava, May 24 2011
G.f.: x*(2+x)/(1-2*x-5*x^2). - Bruno Berselli, May 24 2011
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MATHEMATICA
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LinearRecurrence[{2, 5}, {2, 5}, 40]
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PROG
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(Maxima) a[1]:2$ a[2]:5$ a[n]:=2*a[n-1]+5*a[n-2]$ makelist(a[n], n, 1, 26); [Bruno Berselli, May 24 2011]
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CROSSREFS
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Cf. A000045, A000079, A105476, A159612, A080040, A135522, A103435, A189732, A189735, A189736, A189737, A189738, A189739, A189741, A189742, A189743, A189744, A189745, A189746, A189747, A189748, A189749.
Sequence in context: A124264 A274239 A271858 * A221678 A297350 A027041
Adjacent sequences: A189731 A189732 A189733 * A189735 A189736 A189737
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KEYWORD
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nonn
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AUTHOR
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Harvey P. Dale, Apr 26 2011
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STATUS
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approved
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