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A001504 a(n) = (3n+1)(3n+2). 4
2, 20, 56, 110, 182, 272, 380, 506, 650, 812, 992, 1190, 1406, 1640, 1892, 2162, 2450, 2756, 3080, 3422, 3782, 4160, 4556, 4970, 5402, 5852, 6320, 6806, 7310, 7832, 8372, 8930, 9506, 10100, 10712, 11342, 11990, 12656, 13340, 14042, 14762, 15500, 16256, 17030 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

The oblong numbers (A002378) not divisible by 3. - Gionata Neri, May 10 2015

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

Sum_{k>=0} 1/a(k) = (Pi/3)/sqrt(3). - Benoit Cloitre, Aug 20 2002

a(n) = 18*n + a(n-1) with a(0) = 2. - Vincenzo Librandi, Nov 12 2010

MAPLE

A001504:=n->(3*n+1)*(3*n+2): seq(A001504(n), n=0..100); # Wesley Ivan Hurt, Jan 29 2017

MATHEMATICA

Table[(3*n+1)*(3*n+2), {n, 50}] (* Vladimir Joseph Stephan Orlovsky, Jan 22 2012 *)

PROG

(PARI) a(n)=(3*n+1)*(3*n+2) \\ Charles R Greathouse IV, Jun 17 2017

CROSSREFS

Cf. a(n) = A060544(n+1)*2. Subsequence of A002378.

Sequence in context: A059211 A139271 A133217 * A192351 A136905 A230644

Adjacent sequences:  A001501 A001502 A001503 * A001505 A001506 A001507

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane

STATUS

approved

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Last modified December 7 03:00 EST 2019. Contains 329836 sequences. (Running on oeis4.)