OFFSET
0,4
FORMULA
a(n) = A193296(n+1) if n>0.
EXAMPLE
G.f. = x + x^2 + 2*x^3 + 5*x^4 + 15*x^5 + 51*x^6 + 191*x^7 + 773*x^8 + 3338*x^9 + ...
MATHEMATICA
a[ n_] := If[n < 0, 0, SeriesCoefficient[ Nest[ 1 / (1/x - 1 - (# /. x -> #)) &, O[x], Ceiling[n/2]], {x, 0, n}]];
PROG
(PARI) {a(n) = my(A); if( n<0, 0, A = O(x); forstep(k=1, n, 2, A = 1 / (1/x - 1 - subst(A, x, A))); polcoeff(A, n))};
CROSSREFS
KEYWORD
nonn
AUTHOR
Michael Somos, May 12 2018
STATUS
approved