OFFSET
0,2
COMMENTS
Equals column 2 of triangle A325580.
EXAMPLE
G.f.: A(x) = 1 + 3*x + 15*x^2 + 67*x^3 + 336*x^4 + 1767*x^5 + 9873*x^6 + 58221*x^7 + 360930*x^8 + 2345469*x^9 + 15926115*x^10 + 112702725*x^11 + ...
such that
A(x) = 1 + 3*x*(1+x)^3 + 6*x^2*(1+x)^8 + 10*x^3*(1+x)^15 + 15*x^4*(1+x)^24 + 21*x^5*(1+x)^35 + 28*x^6*(1+x)^48 + 36*x^7*(1+x)^63 + 45*x^8*(1+x)^80 + ...
PROG
(PARI) {a(n) = my(A = sum(m=0, n, (m+1)*(m+2)/2 * x^m * (1+x +x*O(x^n))^(m*(m+2)) )); polcoeff(A, n)}
for(n=0, 30, print1(a(n), ", "))
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, May 11 2019
STATUS
approved