A collection of different examples of how to calculate pi using various programming languages. This uses the arccot/Machin's method:
You do arccot(5)-arccot(369)
arccot:
1/n - 1/(3n^3) + 1/(5n^5) ...

So for n = 4:
1/4 - 1/(3(4)^3) + 1/(5(4)^5) + 1/(7(4)^7) + 1/(9(4)^9) 1/4 - 1/(12^3) + 1/(20^5) + 1/(28^7) + 1/(36^9)