From generalized Catalan numbers.

Terms

a(0) =1a(1) =6a(2) =33a(3) =182a(4) =1020a(5) =5814a(6) =33649a(7) =197340a(8) =1170585a(9) =7012200a(10) =42364476a(11) =257854776a(12) =1579730984a(13) =9734161206a(14) =60290077905a(15) =375138262520