a(n) = binomial((n+1)^2,n).A070780a(n) = binomial((n+1)^2,n).Terms a(0) =1a(1) =4a(2) =36a(3) =560a(4) =12650a(5) =376992a(6) =13983816a(7) =621216192a(8) =32164253550External referencesoeis: A070780