Counting Terms in the Binary Lambda Calculus
  In a paper entitled Binary lambda calculus and combinatory logic, John Tromp presents a simple way of encoding lambda calculus terms as binary sequences. In what follows, we study the numbers of binary strings of a given size that represent lambda terms and derive results from their generating functions, especially that the number of terms of size n grows roughly like 1.963447954^n. 
Katarzyna Grygiel, Pierre Lescanne (LIP)
cs.LO cs.DM cs.DS