Number of essentially parallel achiral series-parallel networks with n elements.

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =8a(5) =18a(6) =37a(7) =84a(8) =180a(9) =413a(10) =902a(11) =2084a(12) =4628a(13) =10726a(14) =24128a(15) =56085a(16) =127421a(17) =296955a(18) =680092a(19) =1588665a(20) =3662439a(21) =8574262a(22) =19875081a(23) =46628789a(24) =108584460a(25) =255264307a(26) =596774173a(27) =1405626896a(28) =3297314994a(29) =7780687159