Generalized Catalan numbers C(4; n).

Terms

a(0) =1a(1) =1a(2) =5a(3) =41a(4) =413a(5) =4641a(6) =55797a(7) =702297a(8) =9137549a(9) =121909457a(10) =1658755685a(11) =22929591433a(12) =321111942781