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 A152773 3 times heptagonal numbers: a(n) = 3n(5n-3)/2. 16
 0, 3, 21, 54, 102, 165, 243, 336, 444, 567, 705, 858, 1026, 1209, 1407, 1620, 1848, 2091, 2349, 2622, 2910, 3213, 3531, 3864, 4212, 4575, 4953, 5346, 5754, 6177, 6615, 7068, 7536, 8019, 8517, 9030, 9558, 10101, 10659, 11232, 11820 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Also the number of 6-cycles in the (n+5)-triangular honeycomb acute knight graph. - Eric W. Weisstein, Jun 25 2017 LINKS Ivan Panchenko, Table of n, a(n) for n = 0..1000 Eric Weisstein's World of Mathematics, Graph Cycle Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA a(n) = (15n^2 - 9n)/2 = A000566(n)*3. a(n) = a(n-1)+15*n-12 with n>0, a(0)=0. - Vincenzo Librandi, Nov 26 2010 G.f.: 3*x*(1+4*x)/(1-x)^3. - Bruno Berselli, Jan 21 2011 a(0)=0, a(1)=3, a(2)=21, a(n)=3*a(n-1)-3*a(n-2)+a(n-3). - Harvey P. Dale, May 08 2012 a(n) = n + A226489(n). - Bruno Berselli, Jun 11 2013 MATHEMATICA Table[3 n (5 n - 3)/2, {n, 0, 50}] (* Harvey P. Dale, May 08 2012 *) LinearRecurrence[{3, -3, 1}, {0, 3, 21}, 50] (* Harvey P. Dale, May 08 2012 *) CoefficientList[Series[-((3 x^5 (1 + 4 x))/(-1 + x)^3), {x, 0, 20}], x] (* Eric W. Weisstein, Jun 25 2017 *) PROG (PARI) a(n)=3*n*(5*n-3)/2 \\ Charles R Greathouse IV, Sep 24 2015 CROSSREFS Cf. A000566, A135706. 3 times n-gonal numbers: A045943, A033428, A062741, A094159, A152751, A152759, A152767, A153783, A153448, A153875. Cf. numbers of the form n*(n*k-k+6))/2, this sequence is the case k=15: see Comments lines of A226492. Cf. A002378 (3-cycles in triangular honeycomb acute knight graph), A045943 (4-cycles), A028896 (5-cycles). Sequence in context: A027499 A303834 A340687 * A039595 A033567 A181156 Adjacent sequences:  A152770 A152771 A152772 * A152774 A152775 A152776 KEYWORD nonn,easy AUTHOR Omar E. Pol, Dec 13 2008 STATUS approved

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Last modified June 17 05:25 EDT 2021. Contains 345080 sequences. (Running on oeis4.)