A174687 Central coefficients T(2n,n) of the Catalan triangle A033184.
1, 2, 9, 48, 275, 1638, 9996, 62016, 389367, 2466750, 15737865, 100975680, 650872404, 4211628008, 27341497800, 177996090624, 1161588834303, 7596549816030, 49772989810635, 326658445806000, 2147042307851595, 14130873926790390, 93115841412899760
Offset: 0
Links
- Alois P. Heinz, Table of n, a(n) for n = 0..370
- Paul Barry, On the Central Coefficients of Riordan Matrices, Journal of Integer Sequences, 16 (2013), Article 13.5.1.
- Dmitry Kruchinin and Vladimir Kruchinin, A Method for Obtaining Generating Function for Central Coefficients of Triangles, Journal of Integer Sequence, Vol. 15 (2012), Article 12.9.3.
- Ran Pan, Exercise L, Project P
- Anssi Yli-Jyrä and Carlos Gómez-Rodríguez, Generic Axiomatization of Families of Noncrossing Graphs in Dependency Parsing, arXiv:1706.03357 [cs.CL], 2017.
Programs
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Magma
[(n+1)*Binomial(3*n,n)/(2*n+1): n in [0..25]]; // Vincenzo Librandi, Apr 08 2015
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Maple
a:= n-> binomial(3*n,n)*(n+1)/(2*n+1): seq(a(n), n=0..25); # Alois P. Heinz, Aug 15 2012
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Mathematica
Table[Binomial[3n,n](n+1)/(2n+1), {n, 0, 25}] (* Vincenzo Librandi, Apr 08 2015 *)
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PARI
a(n) = (n+1)*binomial(3*n,n)/(2*n+1); \\ Michel Marcus, Nov 12 2022
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SageMath
[(n+1)*binomial(3*n,n)/(2*n+1) for n in range(31)] # G. C. Greubel, Nov 09 2022
Formula
a(n) = (n+1)*C(3*n, n)/(2n+1) = (n+1)*[x^(n+1)]( Rev(x/c(x)) ) = (n+1)*A001764(n), c(x) the g.f. of A000108.
G.f.: A(x) = sin(arcsin((3^(3/2)*sqrt(x))/2)/3)/(sqrt(3)*sqrt(x)) + cos(arcsin((3^(3/2)* sqrt(x))/2)/3)/(2*sqrt(1-(27*x)/4)). - Vladimir Kruchinin, May 25 2012
2*n*(2*n+1)*a(n) = 3*(13*n^2 -10*n +1)*a(n-1) -9*(3*n-4)*(3*n-5)*a(n-2). - R. J. Mathar, Nov 24 2012
a(n) = [x^n] ((1 - sqrt(1 - 4*x))/(2*x))^(n+1). - Ilya Gutkovskiy, Nov 01 2017
a(n) ~ 3^(3*n+1/2) / (4^(n+1) * sqrt(Pi*n)). - Amiram Eldar, Aug 29 2025
Comments