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A001513 (6n+1)(6n+5). 2
5, 77, 221, 437, 725, 1085, 1517, 2021, 2597, 3245, 3965, 4757, 5621, 6557, 7565, 8645, 9797, 11021, 12317, 13685, 15125, 16637, 18221, 19877, 21605, 23405, 25277, 27221, 29237, 31325, 33485, 35717, 38021, 40397, 42845, 45365, 47957, 50621, 53357, 56165 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

Sum_{k>=0} 1/a(k) = Pi/(8*sqrt(3)) = 0.22672492... - Jaume Oliver Lafont, May 30 2010

LINKS

T. D. Noe, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (3,-3,1).

FORMULA

a(n) = 72*n + a(n-1) with a(0)=5. - Vincenzo Librandi, Nov 12 2010

G.f. ( -5-62*x-5*x^2 ) / (x-1)^3. - R. J. Mathar, Jan 19 2013

PROG

(PARI) a(n)=(6*n+1)*(6*n+5) \\ Charles R Greathouse IV, Jun 17 2017

CROSSREFS

Sequence in context: A202607 A222533 A059856 * A028556 A214867 A039753

Adjacent sequences:  A001510 A001511 A001512 * A001514 A001515 A001516

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane.

STATUS

approved

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Last modified October 17 18:48 EDT 2018. Contains 316293 sequences. (Running on oeis4.)