Number of unlabeled 4-gonal cacti having n polygons.

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =11a(5) =52a(6) =307a(7) =1936a(8) =13207a(9) =93496a(10) =683988a(11) =5127163a(12) =39230669a(13) =305299420a(14) =2410624122a(15) =19273255184a(16) =155780437711