Catalan numbers - 2 (A120304) with first three terms changed to 1,1,1.

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =12a(5) =40a(6) =130a(7) =427a(8) =1428a(9) =4860a(10) =16794a(11) =58784a(12) =208010a(13) =742898a(14) =2674438a(15) =9694843a(16) =35357668a(17) =129644788a(18) =477638698a(19) =1767263188a(20) =6564120418a(21) =24466267018a(22) =91482563638a(23) =343059613648