Gregory's series for , truncated at 500,000 terms gives to forty places
Only the underlined digits are wrong. This is explained by the following Theorem.
Gregory's series requires more terms than there are particles in the universe to compute 100 digits of .
However, with N = 200,000 and correcting using the first thousand even Euler numbers gives over 5,000 digits of .
See Pi, Euler numbers and asymptotic expansions by J. Borwein, P. Borwein & K. Dilcher in the MAA Monthly 96 (1989) 681-687.