OFFSET
0,2
LINKS
Vladimir Kruchinin, The method for obtaining expressions for coefficients of reverse generating functions, arXiv:1211.3244 [math.CO], 2012.
FORMULA
a(n) = sum(k=1..2*n, (2*n+k)!*sum(j=1..k, sum(l=0..j-1, ((-1)^(n+l+j)*sum(i=j-l..2*n-l+j, (2^i*Stirling1(i,j-l)*binomial(2*n-l+j-1,i-1))/i!))/l!)/(k-j)!)), n>0, a(0)=1.
a(n) ~ 2^(2*n+1) * n^(2*n) / (exp(2*n) * (Pi/2-1)^(2*n+1/2)). - Vaclav Kotesovec, Jan 02 2014
MATHEMATICA
Table[n!*SeriesCoefficient[InverseSeries[Series[2*ArcTan[x]-x, {x, 0, 41}], x], {x, 0, n}], {n, 1, 41, 2}] (* Vaclav Kotesovec, Jan 02 2014 *)
PROG
(Maxima) a(n):=if n=0 then 1 else sum((2*n+k)!*sum(sum(((-1)^(n+l+j)*sum((2^i*stirling1(i, j-l)*binomial(2*n-l+j-1, i-1))/i!, i, j-l, 2*n-l+j))/l!, l, 0, j-1)/(k-j)!, j, 1, k), k, 1, 2*n);
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Kruchinin, Feb 05 2012
STATUS
approved