The formula is p(n) = p(n-1) + 4*((-1)^(n-1))/(2n-1) n = {1,2,3...} and p(0)=0 I think that p(n)-p(n-1) must be less than the precision you want (0.00001)

The formula is p(n) = p(n-1) + 4*((-1)^(n-1))/(2n-1) n = {1,2,3...} and p(0)=0 I think that p(n)-p(n-1) must be less than the precision you want (0.00001). *Mental note: never start reply math on iPad ;)