OFFSET
1,3
FORMULA
a(1) = 1; a(n) = Sum_{k=1..floor(n/2)} binomial(n-1,2*k-1) * a(k). -Ilya Gutkovskiy,Apr 07 2022
EXAMPLE
A(x) = x + x^2 + 2*x^3 + 4*x^4 + 8*x^5 + 17*x^6 + 38*x^7 + 88*x^8 +...
PROG
(PARI) {a(n)=local(F=x^2/(1-x+x*O(x^n))^2, A=x); if(n<1, 0, for(i=1, #binary(n), A=x+subst(A, x, F)); polcoeff(A, n))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna,Jun 08 2006
STATUS
approved