Update 'README.md'

README.md

@@ -27,7 +27,7 @@ ___
 
 ## [Reading Stack](backlog.md)
 - [Formula for Primes](https://en.wikipedia.org/wiki/Formula_for_primes)
-- [Catalan Numbers](https://en.wikipedia.org/wiki/Catalan_number
+- [Catalan Numbers](https://en.wikipedia.org/wiki/Catalan_number)
 - [Spinor](https://en.wikipedia.org/wiki/Spinor)