@article{Bapiraju1994, 
     author = "Bapiraju, Vinnakota and Rao, V.V.Bapeswara", 
     doi = "10.1016/0020-0190(94)00083-2", 
     issn = "00200190", 
     journal = "Information Processing Letters", 
     keyword = "Binary tree enumeration,Combinatorial problems", 
     link = "http://www.sciencedirect.com/science/article/pii/0020019094000832 http://linkinghub.elsevier.com/retrieve/pii/0020019094000832", 
     month = "aug", 
     number = "3", 
     pages = "125--127", 
     title = "Enumeration of binary trees", 
     uri = "http://www.sciencedirect.com/science/article/pii/0020019094000832", 
     volume = "51", 
     year = "1994", 
}

Problems: 333