a(n) = (2n)^(2n) - (2n-1)!*(3n)!/((n-1)!*(2n)!).

A111682

a(n) = (2n)^(2n) - (2n-1)!*(3n)!/((n-1)!*(2n)!).

Terms

    a(0) =1a(1) =76a(2) =16416a(3) =6798016a(4) =4551356800

External references