Inverse Weigh transform of A000085.

Terms

a(0) =1a(1) =2a(2) =2a(3) =7a(4) =14a(5) =43a(6) =130a(7) =446a(8) =1544a(9) =5773a(10) =22170a(11) =89356a(12) =370198a(13) =1591379a(14) =7020014a(15) =31922981a(16) =148679262a(17) =710828036a(18) =3474337098a(19) =17379964444a(20) =88739068866a(21) =462670294023