Number of 2-trees rooted at an edge.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =83a(5) =356a(6) =1599a(7) =7434a(8) =35381a(9) =171508a(10) =843419a(11) =4197179a(12) =21094355a(13) =106915928a(14) =545859112a(15) =2804656069a(16) =14491370996a(17) =75248398034a(18) =392476363133