a(n) = self-convolution of row n of Catalan triangle (A008315).

Terms

a(0) =1a(1) =2a(2) =4a(3) =13a(4) =26a(5) =100a(6) =196a(7) =820a(8) =1581a(9) =6954a(10) =13244a(11) =60214a(12) =113620a(13) =528840a(14) =990756a(15) =4692780a(16) =8741876a(17) =41970280a(18) =77824912a(19) =377687453a(20) =697689538a(21) =3415756084a(22) =6289798684a(23) =31018849628a(24) =56964451670a(25) =282658474700a(26) =517885177320