a(n) = T(0,n)+T(1,n-1)+...+T(n,0), array T given by A048505.

Terms

a(0) =1a(1) =3a(2) =13a(3) =54a(4) =190a(5) =587a(6) =1659a(7) =4412a(8) =11244a(9) =27785a(10) =67089a(11) =159106a(12) =371930a(13) =859159a(14) =1964855a(15) =4454968a(16) =10025240a(17) =22411221a(18) =49804909a(19) =110097630a(20) =242217766a(21) =530575683a(22) =1157623603a(23) =2516577524a(24) =5452589700a(25) =11777599457