Number of unlabeled strongly connected digraphs with n arcs.

Terms

a(0) =1a(1) =0a(2) =1a(3) =1a(4) =3a(5) =6a(6) =25a(7) =91a(8) =442a(9) =2241a(10) =12591a(11) =75180a(12) =478648a(13) =3211245a(14) =22635956a(15) =166828221a(16) =1281518573a(17) =10229858290a(18) =84652925554a(19) =724601312400