Erroneous version of A304932.

Terms

a(0) =1a(1) =2a(2) =6a(3) =20a(4) =87a(5) =420a(6) =2254a(7) =12676a(8) =73819a(9) =438795a(10) =2649555a(11) =16217883a(12) =99888892a(13) =621428188a(14) =3893646748a(15) =24548337096