# Applying the Explicit Formula

It's quite some time since we arrived at Riemann's main result, the explicit formula

where $J(x)$ is the prime power counting function introduced even earlier. It's high time we applied this!

First, let's take a look at $J(x)$ when calculating it exactly:

We've seen the calculus version

of the Euler product, and we know how to express $\xi(s)$ as a product over its roots

where

High time we put everything together -- the reward will be the long expected explicit formula for counting primes! Continue reading Integral Madness

# More symmetry and Another Product

We've seen that $\zeta(s)$ satisfies the functional equation

(Well, it still needs to be proved, but let's just assume it's correct for now.) The goal of this post is an even more symmetrical form that will yield the function $\xi(s)$ which we can develop into an incredibly useful product expression.

On our wish list for $\xi(s)$ we find three items:

1. It's  an entire function, i.e., a function that's holomorphic everywhere in $\mathbb{C}$ without any poles.
2. It has zeros for all non-trivial zeros of the $\zeta$-function, and no others.
3. It's perfectly symmetrical along the critical line, i.e., it satisfies $\xi(1-s)=\xi(s)$.