Number of rooted unlabeled 4-cactus graphs on 3n+1 nodes.

Terms

a(0) =1a(1) =1a(2) =3a(3) =11a(4) =46a(5) =208a(6) =1002a(7) =5012a(8) =25863a(9) =136519a(10) =733902a(11) =4003475a(12) =22106155a(13) =123313289a(14) =693871975a(15) =3933700703a(16) =22447035938a(17) =128828019447a(18) =743142630614