Related to enumeration of edge-rooted catafusenes.

Terms

a(0) =0a(1) =1a(2) =5a(3) =21a(4) =86a(5) =355a(6) =1488a(7) =6335a(8) =27352a(9) =119547a(10) =528045a(11) =2353791a(12) =10575810a(13) =47849685a(14) =217824285a(15) =996999525a(16) =4585548680a(17) =21182609875a(18) =98236853415a(19) =457211008415