OFFSET
0,2
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..375
FORMULA
E.g.f.: A(x)^2, where A(x) is the e.g.f. of the sequence A209305.
MATHEMATICA
(* Expansion of the generating series *) CoefficientList[Series[(InverseErf[(2Exp[x]-2+Exp[1]Sqrt[Pi]Erf[1])/(Exp[1]Sqrt[Pi])])^2, {x, 0, 40}], x]Table[n!, {n, 0, 40}]
(* Recurrence *)
a[n_] := a[n] = a[n-1]+2Sum[Binomial[n-2, k]a[k]b[n-2-k], {k, 0, n-2}];
a[1] = 1;
a[0] = 1;
b[n_] := Sum[Binomial[n, k]a[k+1]a[n-k+1], {k, 0, n}];
Table[Sum[Binomial[n, k]a[k]a[n - k], {k, 0, n}], {n, 0, 12}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Emanuele Munarini, Jan 18 2013
STATUS
approved