Machin-like formulae
M000378
$$\pi=20\arctan\left(\frac{1}{7}\right)+8\arctan\left(\frac{1}{26}\right)-8\arctan\left(\frac{1}{2057}\right)$$
Compact formula
20[7] + 8[26] - 8[2057]
Lehmer's measure
2.19184
References
EULER1779?)
(full reference coming soon)