A simple recurrence with one error.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =85a(5) =430a(6) =2586a(7) =18109a(8) =144880a(9) =1303929a(10) =13039300a(11) =143432311a(12) =1721187744a(13) =22375440685a(14) =313256169604