1. Motzkin numbers;Aigner;European J. Combin.,1998
2. Riordan Arrays: A Primer;Barry,2016
3. On some (pseudo) involutions in the Riordan group;Cameron;J. Integer Seq.,2005
4. Motzkin numbers;Donaghey;J. Combin. Theory Ser. A,1977
5. Enumerative aspects of secondary structures;Došlić;Discrete Math.,2004