OFFSET
1,2
COMMENTS
Compare g.f. to a g.f of the Catalan numbers:
. 1 = Sum_{n>=0} A000108(n)*x^n * Sum_{k>=0} C(2n+k,k)*(-x)^k.
LINKS
Vaclav Kotesovec, Table of n, a(n) for n = 1..260
FORMULA
a(n) = A181167(n)/C(2n,n-1) for n>=1.
a(n) ~ (n!)^2 * (2/BesselJZero[0,1])^(2*n+2), where BesselJZero[0,1] = A115368 = 2.40482555769... . - Vaclav Kotesovec, Jul 31 2014
EXAMPLE
Illustrate the g.f. by the series:
1 = (1 - x + x^2 - x^3 + x^4 - x^5 + x^6 - x^7 +...)
+ 1*1*1*x*(1 - 3^2*x + 6^2*x^2 - 10^2*x^3 + 15^2*x^4 +...)
+ 2*2*2*x^2*(1 - 5^2*x + 15^2*x^2 - 35^2*x^3 + 70^2*x^4 +...)
+ 3*5*11*x^3*(1 - 7^2*x + 28^2*x^2 - 84^2*x^3 + 210^2*x^4 +...)
+ 4*14*114*x^4*(1 - 9^2*x + 45^2*x^2 - 165^2*x^3 + 495^2*x^4 +...)
+ 5*42*1892*x^5*(1 - 11^2*x + 66^2*x^2 - 286^2*x^3 + 1001^2*x^4 +...)
+ 6*132*45800*x^6*(1 - 13^2*x + 91^2*x^2 - 455^2*x^3 + 1820^2*x^4 +...)
+ 7*429*1520535*x^7*(1 - 15^2*x + 120^2*x^2 - 680^2*x^3 + 3060^2*x^4+..) +...
which indicates a connection of this sequence to the Catalan numbers.
MATHEMATICA
nmax=20; Table[(CoefficientList[Series[BesselJ[1, 2*x]/x/BesselJ[0, 2*x], {x, 0, 2*nmax}], x]*Range[0, 2*nmax]!)[[2*n+1]] / Binomial[2n, n-1], {n, 1, nmax}] (* Vaclav Kotesovec, Jul 31 2014 *)
PROG
(PARI) {a(n)=if(n<1, 0, ((-1)^(n-1)-polcoeff(sum(m=0, n-1, a(m)*binomial(2*m, m-1)*x^m*sum(k=0, n-m, binomial(2*m+k, k)^2*(-x)^k)+x*O(x^n)), n))/binomial(2*n, n-1))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Oct 08 2010
STATUS
approved