Hutton's Formula

The Machin-Like Formula

$${\textstyle{1\over 4}}\pi=2\tan^{-1}({\textstyle{1\over 3}})+\tan^{-1}({\textstyle{1\over 7}}).$$

The other two-term Machin-Like Formulas are Euler's Machin-Like Formula, Hermann's Formula, and Machin's Formula.