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A189734 a(1)=2,  a(2)=5, a(n)=2*a(n-1) + 5*a(n-2). 13
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..100

Index entries for linear recurrences with constant coefficients, signature (2, 5).

FORMULA

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

MATHEMATICA

LinearRecurrence[{2, 5}, {2, 5}, 40]

PROG

(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]

CROSSREFS

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

KEYWORD

nonn

AUTHOR

Harvey P. Dale, Apr 26 2011

STATUS

approved

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Last modified April 14 21:21 EDT 2021. Contains 342962 sequences. (Running on oeis4.)