OFFSET
0,5
FORMULA
EXAMPLE
A(x) = 1 + x + x^2 + x^3 + 8*x^4 + 27*x^5 + 64*x^6 + 216*x^7 +...
Take the cube-root of each term, a(n)^(1/3) and
let B(x) be the g.f. of the resulting sequence:
B(x) = 1 + x + x^2 + x^3 + 2*x^4 + 3*x^5 + 4*x^6 + 6*x^7 + 9*x^8 +...
Then 1/B(x) = 1 - x*A(x^3):
1/B(x) = 1 - x - x^4 - x^7 - x^10 - 8*x^13 - 27*x^16 - 64*x^19 -...
PROG
(PARI) {a(n)=if(n==0, 1, sum(k=0, n\3, polcoeff(x^(n-3*k)*(sum(j=0, k, a(j)*x^(3*j))+x*O(x^n))^(n-3*k), n))^3)}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Aug 14 2006
STATUS
approved