Number of 2-trees rooted at a triangle.

Terms

a(0) =1a(1) =1a(2) =3a(3) =10a(4) =39a(5) =164a(6) =746a(7) =3474a(8) =16658a(9) =81166a(10) =401169a(11) =2004517a(12) =10110757a(13) =51402250a(14) =263133142a(15) =1355126922a(16) =7016115632a(17) =36498130908a(18) =190673015083a(19) =999932115039