Partial sums of A000608.

Terms

a(0) =1a(1) =2a(2) =3a(3) =6a(4) =16a(5) =60a(6) =298a(7) =1948a(8) =16460a(9) =179801a(10) =2540520a(11) =46485494a(12) =1101504593a(13) =33766488831