Number of 2-trees rooted at a triangle with 3 similar edges.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =21a(5) =83a(6) =356a(7) =1599a(8) =7434a(9) =35381a(10) =171508a(11) =843419a(12) =4197179a(13) =21094355a(14) =106915928a(15) =545859112a(16) =2804656069a(17) =14491370996a(18) =75248398034a(19) =392476363133