ELI5: Explain Like I'm 5

Perron's formula

Perron's formula basically helps us find out how many times a certain number appears in the sequence of primes.

Okay, so let's say you have a very long sequence of numbers, all of which are prime except for one: 9. You want to know how many times 9 appears in this sequence.

Now, this sequence is really long and it would take forever to count each number yourself. Lucky for us, Perron's formula can help!

First, we need to know something called the Riemann zeta function. This is a really complicated formula that has to do with prime numbers. Don't worry if you don't understand it, most adults don't either!

Next, we use Perron's formula to look at the Riemann zeta function in a new way. We can think of the function as a super long sum of numbers, and each of those numbers is multiplied by a special formula that depends on the number we're trying to count (in our case, 9).

We take this big sum and plug it into Perron's formula, which simplifies things and gives us an answer for how many times 9 appears in the sequence of primes.

So, the next time you want to count how many times a number appears in a sequence of primes, just remember Perron's formula!