I found the formula for $\pi(x)$ on https://en.wikipedia.org/wiki/Skewes%27_number
$$\pi (x)=\operatorname {li} (x)-{\frac {\operatorname {li} ({\sqrt {x}})}{2}}-\sum _{\rho }\operatorname {li} (x^{\rho })+{\text{smaller terms}}$$ What are the smaller terms?