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A196472 a(1)=1; a(n) = floor((3 + sqrt(21))*a(n-1)/2) for n > 1. 1
1, 3, 11, 41, 155, 587, 2225, 8435, 31979, 121241, 459659, 1742699, 6607073, 25049315, 94969163, 360055433, 1365073787, 5175387659, 19621384337, 74390315987, 282035100971, 1069276250873 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Contains only odd numbers.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..150

Index entries for linear recurrences with constant coefficients, signature (4,0,-3)

FORMULA

G.f.: -x*(-1+ x + x ^2) / ( (x-1)*(3*x^2 + 3*x - 1) ). - R. J. Mathar, Oct 04 2011

a(n) = (3 + 2*A108306(n))/15. - R. J. Mathar, Oct 04 2011

MATHEMATICA

With[{c=(3+Sqrt[21])/2}, NestList[Floor[c*#]&, 1, 30]] (* Harvey P. Dale, Apr 23 2014 *)

PROG

(MAGMA) I:=[1, 3, 11]; [n le 3 select I[n] else 4*Self(n-1)-3*Self(n-3): n in [1..30]]: // Vincenzo Librandi, Oct 05 2011

CROSSREFS

Sequence in context: A281593 A113437 A076540 * A258471 A176085 A129637

Adjacent sequences:  A196469 A196470 A196471 * A196473 A196474 A196475

KEYWORD

nonn,easy

AUTHOR

Philippe Deléham, Oct 03 2011

STATUS

approved

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Last modified January 19 06:18 EST 2022. Contains 350464 sequences. (Running on oeis4.)