M000009120

$$\pi=8\arctan\left(\frac{1}{3}\right)-4\arctan\left(\frac{1}{4}\right)+8\arctan\left(\frac{1}{5}\right)-4\arctan\left(\frac{1}{18}\right)+4\arctan\left(\frac{1}{21}\right)$$

Compact formula	`8[3] - 4[4] + 8[5] - 4[18] + 4[21]`
Lehmer's measure	6.74048