Generates pi, using the formula:

Pi=16*arctan(1/5)-4*arctan(1/239)

and leaves the result in an array \xr, printing what it’s calculated as it goes along.

The number of digits you can compute depends on your implementation of TeX. The last digit may be wrong, and if it's 0 or 9, the penultimate digit may also be wrong.

The author is Denis B. Roegel.