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 A139276 a(n) = n*(8*n+3). 9
 0, 11, 38, 81, 140, 215, 306, 413, 536, 675, 830, 1001, 1188, 1391, 1610, 1845, 2096, 2363, 2646, 2945, 3260, 3591, 3938, 4301, 4680, 5075, 5486, 5913, 6356, 6815, 7290, 7781, 8288, 8811, 9350, 9905, 10476, 11063, 11666, 12285, 12920 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Sequence found by reading the line from 0, in the direction 0, 11,..., in the square spiral whose vertices are the triangular numbers A000217. Opposite numbers to the members of A139272 in the same spiral. LINKS G. C. Greubel, Table of n, a(n) for n = 0..5000 Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA a(n) = 8*n^2 + 3*n. Sequences of the form a(n)=8*n^2+c*n have generating functions x{c+8+(8-c)x} / (1-x)^3 and recurrence a(n)= 3a(n-1)-3a(n-2)+a(n-3). The inverse binomial transform is 0, c+8, 16, 0, 0, ... (0 continued). This applies to A139271-A139278, positive or negative c. - R. J. Mathar, May 12 2008 a(n) = 16*n+a(n-1)-5 (with a(0)=0). - Vincenzo Librandi, Aug 03 2010 From G. C. Greubel, Jul 18 2017: (Start) G.f.: x*(5*x + 11)/(1-x)^3. E.g.f.: (8*x^2 + 11*x)*exp(x). (End) EXAMPLE a(1)=16*1+0-5=11; a(2)=16*2+11-5=38; a(3)=16*3+38-5=81. - Vincenzo Librandi, Aug 03 2010 MATHEMATICA a[n_]:=n*(8*n+3); a[Range[0, 60]] (* Vladimir Joseph Stephan Orlovsky, Feb 05 2011*) PROG (PARI) a(n)=n*(8*n+3) \\ Charles R Greathouse IV, Jun 16 2017 CROSSREFS Cf. A000217, A014634, A014635, A033585, A033586, A033587, A035008, A051870, A069129, A085250, A072279, A139272, A139273, A139274, A139275, A139277, A139278, A139279, A139280, A139281, A139282. Sequence in context: A071853 A072313 A063146 * A010002 A143109 A007585 Adjacent sequences:  A139273 A139274 A139275 * A139277 A139278 A139279 KEYWORD easy,nonn AUTHOR Omar E. Pol, Apr 26 2008 STATUS approved

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Last modified May 25 19:29 EDT 2019. Contains 323576 sequences. (Running on oeis4.)