OFFSET
0,2
COMMENTS
The logarithmic derivative equals 3 times A202144.
Radius of convergence r is approximately equal to:
r = 0.29292898163912377571341042979083759105819894028205070...
where limit a(n)*r^n = 0.81375788478450306387071671675851320912210...
EXAMPLE
G.f.: A(x) = 1 + 3*x + 9*x^2 + 32*x^3 + 111*x^4 + 378*x^5 + 1287*x^6 +...
where 1/A(x) = 1 - 3*x - 5*x^3 + 7*x^6 + 9*x^10 - 11*x^15 - 13*x^21 + 15*x^28 + 17*x^36 +...+ (2*n+1)*(-x)^(n*(n+1)/2) +...
Compare g.f. A(x) to the cube of the partition function:
P(x)^3 = 1 + 3*x + 9*x^2 + 22*x^3 + 51*x^4 + 108*x^5 + 221*x^6 +...
where 1/P(x)^3 = 1 - 3*x + 5*x^3 - 7*x^6 + 9*x^10 - 11*x^15 + 13*x^21 - 15*x^28 + 17*x^36 +...+ (-1)^n*(2*n+1)*x^(n*(n+1)/2) +...
PROG
(PARI) {a(n)=polcoeff(1/sum(k=0, sqrtint(2*n+1), (2*k+1)*(-x)^(k*(k+1)/2) +x*O(x^n)), n)}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Dec 12 2011
STATUS
approved