a(n) = n * Sum_{d|n} binomial(d+n-1,n)/d.

Terms

a(0) =1a(1) =5a(2) =13a(3) =49a(4) =131a(5) =545a(6) =1723a(7) =6809a(8) =24484a(9) =94445a(10) =352727a(11) =1366273a(12) =5200313a(13) =20135939a(14) =77571083a(15) =301034537a(16) =1166803127a(17) =4540794476a(18) =17672631919a(19) =68943346009a(20) =269129827042