G.f. satisfies: A(x) = 1 / (1/x - 1 - A(A(x))), with A(0) = 0.

Terms

a(0) =0a(1) =1a(2) =1a(3) =2a(4) =5a(5) =15a(6) =51a(7) =191a(8) =773a(9) =3338a(10) =15243a(11) =73131a(12) =366815a(13) =1916260a(14) =10394665a(15) =58404853a(16) =339223859a(17) =2033188222a(18) =12556915219a(19) =79807729238a(20) =521399203037