a(n) = n*(n^2 - 2*n + 4)*binomial(2*n,n)/((n + 1)*(n + 2)).

Terms

a(0) =0a(1) =1a(2) =4a(3) =21a(4) =112a(5) =570a(6) =2772a(7) =13013a(8) =59488a(9) =266526a(10) =1175720a(11) =5123426a(12) =22108704a(13) =94645460a(14) =402503220a(15) =1702300725a(16) =7165821120a(17) =30043474230a(18) =125523450360a(19) =522857438070