a(n) = 2*Sum_{k=0..n-1} C(n-1,k)*C(n+k,k) + n.

Terms

a(0) =0a(1) =3a(2) =10a(3) =41a(4) =196a(5) =1007a(6) =5342a(7) =28821a(8) =157192a(9) =864155a(10) =4780018a(11) =26572097a(12) =148321356a(13) =830764807a(14) =4666890950a(15) =26283115053a(16) =148348809232a(17) =838944980531