for an Ordered Pair (m,n) I use the Encoding Method = ((m+n)(m+n+1)/2)+n for encoding this ordered pair into a single number, this helps me to find an enumeration for functions , so if I have a function that takes 2 arguments an an Input I encode them using this Mathmatical method , But my Question if I want to decode any number in an Ordered Pair , how to do this?

I appreciate your help, I am a master of science in computer science student , and I attend the course of Computability theory.

thanks for all

Caio