Mercury's Orbital Precession Anomaly

The perihelion of Mercury precesses by 5600 arc-seconds per century, which is 43 arc-seconds per century more than Newtonian physics alone would predict

Albert Einstein proposed a second-order correction to Mercury's orbit, based on his general theory of relativity.

Which equation had Einstein used to calculate this?

$$\Delta \phi = 2 l \int_{r_1}^{r_2}\frac{dr}{r^2}\left(1-\frac{2GM}{r c^2}\right)^{-1/2}\left[c^2 e^2 \left(1-\frac{2GM}{r c^2}\right)^{-1} - \left(c^2 + \frac{l^2}{r^2}\right)\right]^{-1/2}$$