login
a(n) = binomial(3n+1, n-1).
11

%I #46 Mar 12 2024 23:49:19

%S 1,7,45,286,1820,11628,74613,480700,3108105,20160075,131128140,

%T 854992152,5586853480,36576848168,239877544005,1575580702584,

%U 10363194502115,68248282427325,449972009097765,2969831763694950,19619725782651120,129728497393775280

%N a(n) = binomial(3n+1, n-1).

%C This sequence is related to A006013 by a(n)/n = A006013(n)/2.

%H Bruno Berselli, <a href="/A236194/b236194.txt">Table of n, a(n) for n = 1..100</a>

%H Emanuele Munarini, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL20/Munarini/muna4.html">Shifting Property for Riordan, Sheffer and Connection Constants Matrices</a>, Journal of Integer Sequences, Vol. 20 (2017), Article 17.8.2.

%F G.f.: (sqrt(4-27*x)*cos((2/3)*arcsin((3/2)*sqrt(3*x))) + sqrt(3*x)*sin((2/3)*arcsin((3/2)*sqrt(3*x))) - sqrt(4-27*x))/(3*sqrt(4-27*x)*x^2). - _Emanuele Munarini_, Oct 14 2014

%F From _Peter Bala_, Nov 04 2015: (Start)

%F With offset 0, the o.g.f. equals f(x)*g(x)^4, where f(x) is the o.g.f. for A005809 and g(x) is the o.g.f. for A001764.

%F 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), A013698 (k = 5), A165817 (k = -1), A117671 (k = -2). (End)

%F a(n) = [x^n] x/(1 - x)^(2*n+3). - _Ilya Gutkovskiy_, Oct 10 2017

%F From _Karol A. Penson_, Mar 02 2024: (Start)

%F G.f.: ((sqrt(3)*sqrt(x)*i + sqrt(4 - 27*x))*(4*sqrt(4 - 27*x) - 12*i*sqrt(3)*sqrt(x))^(2/3) + (-sqrt(3)*sqrt(x)*i + sqrt(4 - 27*x))*(4*sqrt(4 - 27*x) + 12*i*sqrt(3)*sqrt(x))^(2/3) - 8*sqrt(4 - 27*x))/(24*sqrt(4 - 27*x)*x^2), where i is the imaginary unit, i=sqrt(-1).

%F G.f.: hypergeometric3F2([5/3,2,7/3],[5/2,3],27*x/4).

%F G.f. = G satisfies the algebraic equation: 1 + (7*z-1)*G + (27*z-4)*z^2*G^2 + (27*z-4)*z^4*G^3 = 0. (End)

%t Table[Binomial[3n+1, n-1], {n, 30}]

%o (Magma) [Binomial(3*n+1,n-1): n in [1..30]];

%o (Maxima) makelist(binomial(3*n+4,n),n,0,40); /* _Emanuele Munarini_, Oct 14 2014 */

%o (PARI) vector(30, n, binomial(3*n+1, n-1)) \\ _Altug Alkan_, Nov 04 2015

%o (SageMath) [binomial(3*n+1,n-1) for n in range(1,31)] # _G. C. Greubel_, Nov 09 2022

%Y Cf. A006013; A025174: C(3n-1, n-1); A117671: C(3n+1, n+1).

%Y Second column of the triangle A159841.

%Y Third column of the triangle A119301.

%Y Cf. A001764, A004319, A005809, A013698, A045721, A165817.

%Y Cf. A045721, A117671.

%K nonn,easy

%O 1,2

%A _Bruno Berselli_, Jan 20 2014