OFFSET
1,3
COMMENTS
a(n) == 1 (mod 2) iff n = 2^k for k>=0.
LINKS
Paul D. Hanna, Table of n, a(n) for n = 1..300
EXAMPLE
G.f.: A(x) = x + x^2 + 2*x^3 + 7*x^4 + 26*x^5 + 124*x^6 + 596*x^7 +...
The series reversion of A(x) = x - x*[A(x) - A(-x)]/2, thus:
A(x - x^2 - 2*x^4 - 26*x^6 - 596*x^8 - 18954*x^10 -...) = x.
PROG
(PARI) {a(n)=local(A=x+x^2); for(i=0, n, A=serreverse(x-x/2*(A-subst(A, x, -x+x*O(x^n))))) ; polcoeff(A, n)}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Jun 13 2008
STATUS
approved