OFFSET
1,3
FORMULA
G.f.: A(x) = (G(x) - G(-x))/2, where G(x) is the g.f. of A107700 and satisfies: G(G(x)) = x + 2*G(x)^2.
MATHEMATICA
a[n_] := Module[{A, B, F}, A = Series[x+x^2+x^(2*n), {x, 0, 2*n}]; If[n<1, 0, For[i=0, i <= 2*n, i++, F = x+2*A^2; B = InverseSeries[A]; A = (A+(B /. x -> F))/2]; SeriesCoefficient[A, {x, 0, 2*n-1}]]]; Table[a[n], {n, 1, 19}] (* Jean-François Alcover, Feb 04 2014, after PARI *)
PROG
(PARI) {a(n)=local(A, B, F); A=x+x^2+x*O(x^(2*n)); if(n<1, 0, for(i=0, 2*n, F=x+2*A^2; B=serreverse(A); A=(A+subst(B, x, F))/2); polcoeff(A, 2*n-1, x))}
CROSSREFS
KEYWORD
sign
AUTHOR
Paul D. Hanna, May 21 2005
STATUS
approved