Number of planar planted trees with n non-root nodes and without isolated 2-valent nodes.

Terms

a(0) =0a(1) =1a(2) =0a(3) =2a(4) =2a(5) =7a(6) =14a(7) =41a(8) =107a(9) =307a(10) =871a(11) =2546a(12) =7497a(13) =22380a(14) =67366a(15) =204517a(16) =625132a(17) =1922700a(18) =5945469a(19) =18473841a(20) =57649699a(21) =180602285a(22) =567772883a(23) =1790663427a(24) =5663969707a(25) =17963483548a(26) =57112388657a(27) =181994536484a(28) =581168157605