login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A201556 G.f.: exp( Sum_{n>=1} C(2*n^2,n^2) * x^n/n ). 7

%I #23 Jan 27 2017 14:36:59

%S 1,2,37,16278,150303194,25282422428664,73752140616074524401,

%T 3639659041645240391812731402,2993893262520330875797362908273443346,

%U 40656420461436928818704580402413441308206341488,9054851465691640957562090101797213977192016103053025996396

%N G.f.: exp( Sum_{n>=1} C(2*n^2,n^2) * x^n/n ).

%C Self-convolution of A213402.

%C Compare to the g.f. C(x) = 1 + x*C(x)^2 of the Catalan numbers (A000108): C(x)^2 = exp( Sum_{n>=1} binomial(2*n,n) * x^n/n ).

%H G. C. Greubel, <a href="/A201556/b201556.txt">Table of n, a(n) for n = 0..40</a>

%F a(n) = (1/n) * Sum_{k=1..n} C(2*k^2,k^2) * a(n-k) for n>0 with a(0)=1.

%F a(n) ~ 4^(n^2) / (sqrt(Pi)*n^2). - _Vaclav Kotesovec_, Mar 06 2014

%e G.f.: A(x) = 1 + 2*x + 37*x^2 + 16278*x^3 + 150303194*x^4 +...

%e where

%e log(A(x)) = 2*x + 70*x^2/2 + 48620*x^3/3 + 601080390*x^4/4 +...+ C(2*n^2,n^2)*x^n/n +...

%t nmax = 10; b = ConstantArray[0, nmax+1]; b[[1]] = 1; Do[b[[n+1]] = 1/n*Sum[Binomial[2*k^2, k^2]*b[[n-k+1]], {k, 1, n}], {n, 1, nmax}]; b (* _Vaclav Kotesovec_, Mar 06 2014 *)

%o (PARI) {a(n)=polcoeff(exp(sum(m=1,n,binomial(2*m^2,m^2)*x^m/m)+x*O(x^n)),n)}

%o (PARI) {a(n)=if(n==0,1,(1/n)*sum(k=1,n,binomial(2*k^2,k^2)*a(n-k)))}

%Y Cf. A213402, A201555, A000984, A200002, A213409.

%K nonn

%O 0,2

%A _Paul D. Hanna_, Dec 02 2011

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified April 19 16:21 EDT 2024. Contains 371794 sequences. (Running on oeis4.)