OFFSET
0,3
EXAMPLE
G.f.: A(x) = 1 + x + 2*x^2 + 3*x^3 + 6*x^4 + 9*x^5 + 20*x^6 + 31*x^7 + ...
where:
A(x) = 1 + x/(1-x) + x^2/((1-x)^2*(1-x^2)) + x^3/((1-x)^3*(1-x^3)) + x^4/((1-x)^4*(1-x^2)^2*(1-x^4)) + x^5/((1-x)^5*(1-x^5)) + x^6/((1-x)^6*(1-x^2)^3*(1-x^3)^2*(1-x^6)) + ...
PROG
(PARI) {a(n)=local(A=1); A=1+sum(m=1, n, x^m/prod(d=1, m, if(m%d==0, (1-x^d +x*O(x^n))^(m/d), 1))); polcoeff(A, n)}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Jul 17 2011
STATUS
approved