OFFSET
0,3
FORMULA
EXAMPLE
A(x) = 1 + x + 3*x^2 + 8*x^3 + 27*x^4 + 89*x^5 + 300*x^6 +...
1/A(x) = 1 - x - 2*x^2 - 3*x^3 - 10*x^4 - 27*x^5 - 76*x^6 - 212*x^7 -...
1/A(x) = 1 - x*B(x)^2, where
B(x)^2 = 1 + 2*x + 3*x^2 + 10*x^3 + 27*x^4 + 76*x^5 + 212*x^6 +...
and B(x) is the g.f. of A121648 where all coefficients are squares:
B(x) = 1 + x + x^2 + 4*x^3 + 9*x^4 + 25*x^5 + 64*x^6 + 256*x^7 +...
PROG
(PARI) {a(n)=local(B=1+x); if(n==0, 1, for(m=0, n, B=1/(1-x*sum(k=0, m, polcoeff(B, k)^2*x^(2*k))+O(x^(2*n+2)))); polcoeff(B, 2*n))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Aug 14 2006
STATUS
approved