He also published on Logarithmic integral function.

Logarithmic integral function in calculus.

As with the Prime Number Theorem, a more precise estimate may be given in terms of the logarithmic integral function.

In mathematics, the logarithmic integral function or integral logarithm li(x) is a special function.

In mathematics, the Ramanujan-Soldner constant (also called the Soldner constant) is a mathematical constant defined as the unique positive zero of the logarithmic integral function.