Number of unlabeled asymmetric 2-ary cacti having n polygons.

Terms

a(0) =1a(1) =1a(2) =0a(3) =1a(4) =2a(5) =8a(6) =18a(7) =61a(8) =170a(9) =538a(10) =1654a(11) =5344a(12) =17252a(13) =57146a(14) =190786a(15) =646305a(16) =2209050a(17) =7626164a(18) =26532732a(19) =93013852a(20) =328196780a(21) =1165060170a(22) =4158266282a(23) =14915635376a(24) =53745892932a(25) =194477856048a(26) =706436256598