a(n) = Sum_{0<=j<=i<=n} A027113(i, n+j).

Terms

a(0) =1a(1) =4a(2) =13a(3) =40a(4) =119a(5) =350a(6) =1022a(7) =2973a(8) =8635a(9) =25074a(10) =72850a(11) =211875a(12) =616985a(13) =1799092a(14) =5253127a(15) =15358500a(16) =44958889a(17) =131759776a(18) =386557548a(19) =1135204289a(20) =3336791503a(21) =9816315842a(22) =28900431835a(23) =85147344488a(24) =251030187583a(25) =740539502786