Number of tree-rooted planar maps with 3 faces and n vertices and no isthmuses.

Terms

a(0) =2a(1) =15a(2) =60a(3) =175a(4) =420a(5) =882a(6) =1680a(7) =2970a(8) =4950a(9) =7865a(10) =12012a(11) =17745a(12) =25480a(13) =35700a(14) =48960a(15) =65892a(16) =87210a(17) =113715a(18) =146300a(19) =185955a(20) =233772a(21) =290950a(22) =358800a(23) =438750a(24) =532350a(25) =641277a(26) =767340a(27) =912485a(28) =1078800a(29) =1268520