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 A001450 a(n) = binomial(5*n,2*n). 6
 1, 10, 210, 5005, 125970, 3268760, 86493225, 2319959400, 62852101650, 1715884494940, 47129212243960, 1300853625660225, 36052387482172425, 1002596421878664480, 27963143931814663880, 781879430625942976880, 21910242651571684460050, 615167304833936727234180 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS T. D. Noe, Table of n, a(n) for n=0..100 P. Bala, A note on A001450 M. Dziemianczuk, On Directed Lattice Paths With Additional Vertical Steps, arXiv preprint arXiv:1410.5747 [math.CO], 2014 FORMULA a(n) = (5*n)!/((3*n)!*(2*n)!). a(n) = 2F1[-3n,-2n,1,1] (see Mathematica code below). [John M. Campbell, Jul 15 2011] G.f.: hypergeom([1/5, 2/5, 3/5, 4/5], [1/3, 1/2, 2/3], (3125/108)*x). - Robert Israel, Aug 07 2014 From Peter Bala, Oct 05 2015: (Start) a(n) = [x^n] ( (1 + x)*C(x) )^(5*n), where C(x) = (1 - sqrt(1 - 4*x))/(2*x) is the o.g.f. for the Catalan numbers A000108. a(n) = 5*A259550(n) for n >= 1. exp( 1/5 * Sum_{n >= 1} a(n)*x^n/n ) = 1 + 2*x + 23*x^2 + 377*x^3 + ... is the o.g.f. for the sequence of Duchon numbers A060941. (End) a(n) = [x^(2*n)] 1/(1 - x)^(3*n+1). - Ilya Gutkovskiy, Oct 10 2017 MAPLE f := n->(5*n)!/((3*n)!*(2*n)!); MATHEMATICA Table[Hypergeometric2F1[-3n, -2n, 1, 1], {n, 0, 60}] (* John M. Campbell, Jul 15 2011 *) Table[Binomial[5n, 2n], {n, 0, 20}] (* Harvey P. Dale, Nov 09 2011 *) PROG (MAGMA) [Binomial(5*n, 2*n): n in [0..20]]; // Vincenzo Librandi, Aug 07 2014 (PARI) a(n) = binomial(5*n, 2*n) \\ Altug Alkan, Oct 06 2015 CROSSREFS Cf. A001451, A001459, A001460, A000108, A060941, A259550. Sequence in context: A067642 A052245 A052246 * A076803 A120596 A238467 Adjacent sequences:  A001447 A001448 A001449 * A001451 A001452 A001453 KEYWORD nonn,easy AUTHOR STATUS approved

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Last modified January 20 21:36 EST 2019. Contains 319336 sequences. (Running on oeis4.)