Generalized Catalan numbers: a(0) = 1, a(n) = a(n-1) + Sum_{k=1..n-4} a(k) * a(n-k).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =2a(6) =5a(7) =13a(8) =34a(9) =90a(10) =241a(11) =652a(12) =1780a(13) =4899a(14) =13581a(15) =37893a(16) =106340a(17) =299978a(18) =850187a(19) =2419788a(20) =6913658a(21) =19822439a(22) =57015620a(23) =164476023a(24) =475752469a(25) =1379553027a(26) =4009532279a(27) =11678165796a(28) =34081307147a(29) =99646051271