a(n) = (2n)! * (n+1)! / 2^(2n).A202689a(n) = (2n)! * (n+1)! / 2^(2n).Terms a(0) =1a(1) =1a(2) =9a(3) =270a(4) =18900a(5) =2551500a(6) =589396500a(7) =214540326000External referencesoeis: A202689