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 A013698 a(n) = binomial(3*n+2, n-1). 15
 1, 8, 55, 364, 2380, 15504, 100947, 657800, 4292145, 28048800, 183579396, 1203322288, 7898654920, 51915526432, 341643774795, 2250829575120, 14844575908435, 97997533741800, 647520696018735, 4282083008118300 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Degree of variety K_{2,n}^1. Also number of double-rises (or odd-level peaks) in all generalized {(1,2),(1,-1)}-Dyck paths of length 3(n+1). Number of dissections of a convex (2n+2)-gon by n-2 noncrossing diagonals into (2j+2)-gons, 1<=j<=n-1. a(n) is the number of lattice paths from (0,0) to (3n+1,n-1) avoiding two consecutive up-steps. - Shanzhen Gao, Apr 20 2010 LINKS Robert Israel, Table of n, a(n) for n = 1..1000 M. S. Ravi et al., Dynamic Pole Assignment and Schubert Calculus, SIAM J. Control Optimization, 34 (1996), 813-832, esp. p. 825. Daniel W. Stasiuk, An Enumeration Problem for Sequences of n-ary Trees Arising from Algebraic Operads, Master's Thesis, University of Saskatchewan-Saskatoon (2018). FORMULA G.f.: g/((g-1)^3*(3*g-1)) where g*(1-g)^2 = x. - Mark van Hoeij, Nov 09 2011 a(n) = Sum_{k=0..n-1} binomial(2*n+k+2,k). - Arkadiusz Wesolowski, Apr 02 2012 2*(2*n+3)*(n+1)*a(n) -n*(67*n+34)*a(n-1) +30*(3*n-1)*(3*n-2)*a(n-2)=0. - R. J. Mathar, Feb 05 2013 a(n+1) = (3*n+5)*(3*n+4)*(3*n+3)*a(n)/((2*n+5)*(2*n+4)*n). - Robert Israel, Aug 09 2015 From Peter Bala, Nov 04 2015: (Start) With offset 0, the o.g.f. equals f(x)*g(x)^5, where f(x) is the o.g.f. for A005809 and g(x) is the o.g.f. for A001764. More generally, f(x)*g(x)^k is the o.g.f. for the sequence binomial(3*n + k,n). Cf. A045721 (k = 1), A025174 (k = 2), A004319 (k = 3), A236194 (k = 4), A165817 (k = -1), A117671 (k = -2). MAPLE seq(binomial(3*n+2, n-1), n=0..30); # Robert Israel, Aug 09 2015 MATHEMATICA Table[Binomial[3*n+2, n-1], {n, 25}] (* Arkadiusz Wesolowski, Apr 02 2012 *) PROG (PARI) first(m)=vector(m, n, binomial(3*n+2, n-1)); /* Anders Hellström, Aug 09 2015 */ (MAGMA) [Binomial(3*n+2, n-1): n in [1..25]]; // Vincenzo Librandi, Aug 10 2015 (Sage) [binomial(3*n+2, n-1) for n in (1..25)] # G. C. Greubel, Mar 21 2019 (GAP) List([1..25], n-> Binomial(3*n+2, n-1)) # G. C. Greubel, Mar 21 2019 CROSSREFS Cf. A013699 (q=2), A013700 (q=3), A013701 (q=4), A013702 (q=5). A column of triangle A102537. Cf. A001764, A004319, A005809, A006013, A025174, A045721, A117671, A165817, A236194. Sequence in context: A244501 A026994 A110184 * A154245 A143420 A075734 Adjacent sequences:  A013695 A013696 A013697 * A013699 A013700 A013701 KEYWORD nonn,easy AUTHOR Joachim.Rosenthal(AT)nd.edu (Joachim Rosenthal), Emeric Deutsch STATUS approved

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Last modified July 11 20:03 EDT 2020. Contains 335652 sequences. (Running on oeis4.)