1. A Course in Enumeration;Aigner,2007
2. Analytic Combinatorics;Flajolet,2008
3. The Encyclopedia of Integer Sequences;Sloane,1995
4. N. Sloane, Sequence A001006 in the on-line encyclopedia of integer sequences, http://eeis.org/Seis.html.
5. Exchange Symmetries in Motzkin Path and Bargraph Models of Copolymer Adsorption