1,2

M. P. Develin and S. P. Sullivant, Markov Bases of Binary Graph Models, Annals of Combinatorics 7 (2003) 441-466.

C. Poupard, Deux proprietes des arbres binaires ordonnes stricts, European J. Combin., 10 (1989), 369-374.

E.G.F. =$frac 12(3(\sec frac x{\sqrt{2}})^2(tan frac x{\sqrt{2}})^2-frac x{\sqrt{2}}\ (\sec frac x{\sqrt{2}})^2(tan frac x{\sqrt{2}}))\ $

Sequence in context: A051687 A101791 A140034 this_sequence A106907 A020456 A036935

Adjacent sequences: A131635 A131636 A131637 this_sequence A131639 A131640 A131641

nonn

Wenjin W. (wjwoan(AT)hotmail.com), Oct 03 2007