Number of series-parallel networks with n unlabeled edges, multiple edges not allowed.

Terms

a(0) =0a(1) =1a(2) =1a(3) =2a(4) =4a(5) =8a(6) =18a(7) =40a(8) =94a(9) =224a(10) =548a(11) =1356a(12) =3418a(13) =8692a(14) =22352a(15) =57932a(16) =151312a(17) =397628a(18) =1050992a(19) =2791516a(20) =7447972a(21) =19950628a(22) =53635310a(23) =144664640a(24) =391358274a(25) =1061628772a(26) =2887113478a(27) =7869761108a(28) =21497678430a(29) =58841838912