- <A
   HREF="http://www.math.stonybrook.edu/~moira/mat331-spr10/papers/2006%20KoshyParity%20and%20Primality%20of%20Catalan.pdf">A
   proof</A> by Koshy and Salmassi starting from Segner's recurrence formula for the Catalan numbers.
 - <A HREF="https://arxiv.org/abs/math/0611465">A proof</A> by Ji and Wilf using the method of recursive palindromes.