

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(n1) 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



