OFFSET
0,3
COMMENTS
EXAMPLE
G.f.: A(x) = 1 + x + 3*x^2 + 21*x^3 + 263*x^4 + 5165*x^5 + 146335*x^6 +...
where
A(x) = 1 + x/(1+x) + 2!^2*x^2/((1+1*2*x)*(1+2*1*x)) + 3!^2*x^3/((1+1*3*x)*(1+2*2*x)*(1+3*1*x)) + 4!^2*x^4/((1+1*4*x)*(1+2*3*x)*(1+3*2*x)*(1+4*1*x)) + 5!^2*x^5/((1+1*5*x)*(1+2*4*x)*(1+3*3*x)*(1+4*2*x)*(1+5*1*x)) +...
MATHEMATICA
CoefficientList[Series[Sum[(n!)^2 x^n/Product[1+k(n-k+1)x, {k, n}], {n, 0, 20}], {x, 0, 20}], x] (* Harvey P. Dale, Aug 03 2020 *)
PROG
(PARI) {a(n)=polcoeff(sum(m=0, n, m!^2*x^m/prod(k=1, m, 1+(m-k+1)*k*x+x*O(x^n))), n)}
for(n=0, 20, print1(a(n), ", "))
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Jan 03 2013
STATUS
approved