G.f.: 1 = Sum_{n>=0} a(n) * x^n * Sum_{k=0..2*n+1} binomial(2*n+1,k)^2 * (-x)^k.
A217042
G.f.: 1 = Sum_{n>=0} a(n) * x^n * Sum_{k=0..2*n+1} binomial(2*n+1,k)^2 * (-x)^k.
Terms
- a(0) =1a(1) =1a(2) =9a(3) =216a(4) =9685a(5) =690129a(6) =71218224a(7) =10016312400
External references
- oeis: A217042