What is z phi?

Z phi, or the zeta function, typically refers to the Riemann zeta function, which is a complex function denoted as ζ(s). It plays a crucial role in number theory, particularly in the distribution of prime numbers. The function is defined for complex numbers and has a series representation for real parts of s greater than 1, and it can be analytically continued to other values except for s = 1, where it has a simple pole. The Riemann Hypothesis, one of the most important unsolved problems in mathematics, concerns the distribution of its zeros.