a(n) = A136439(n) + Catalan(n).

Terms

a(0) =1a(1) =2a(2) =5a(3) =15a(4) =48a(5) =160a(6) =549a(7) =1924a(8) =6851a(9) =24700a(10) =89945a(11) =330239a(12) =1220884a(13) =4540128a(14) =16968958a(15) =63701573a(16) =240059998a(17) =907760348a(18) =3443048256a(19) =13094812968a(20) =49925646786a(21) =190772846082a(22) =730451716847