Enter the n2. One way would be to enter 20515. If youre using the Casio Scientific Calculator then you should-1.
If n is 5 and r is 3 then nCr 5.
Many of the calculators keys are used to perform more than one function. On the top of the screen youll see a list of the values the calculator computes. If youre using the Casio Scientific Calculator then you should-1. To get out of STAT mode press 15120.