Number of solid 2-trees with 2n+1 edges.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =5a(5) =13a(6) =49a(7) =201a(8) =940a(9) =4643a(10) =24037a(11) =127859a(12) =696365a(13) =3858759a(14) =21704863a(15) =123619126a(16) =711787259a(17) =4137614454a(18) =24256010068a(19) =143271593982a(20) =852001881614