ELI5: Explain Like I'm 5

Hurwitz zeta function

The Hurwitz zeta function is like a special kind of math machine that helps us understand certain numbers in a special way. Let's imagine we have a big line of numbers, like 1, 2, 3, 4, 5, and so on, that goes all the way to infinity. Now, imagine we have a little machine that takes two numbers. The first number can be any positive number you want, let's say 3. The second number can also be any positive number, like 2.

Now, what this little machine does is it takes the first number, in this case, 3, and it does some magic with it. Specifically, it adds up a bunch of fractions where the denominator (the bottom part of the fraction) is the second number, 2. The numerator (the top part of the fraction) starts at 1 and keeps increasing by 1 each time we add a new fraction.

So, with our example of 3 and 2, the Hurwitz zeta function would do this magic calculation:
1/2^3 + 1/3^3 + 1/4^3 + 1/5^3 + ...

That "..." means that we keep adding more fractions with bigger denominators going on forever. Now, depending on the second number you choose, the result of this calculation can be different. For example, if the second number is 1, then our calculation would be:
1/1^3 + 1/2^3 + 1/3^3 + 1/4^3 + ...

But this time, we start with 1/1^3, since 1/1 is just 1. So, the Hurwitz zeta function does this magic calculation for different combinations of the first and second numbers and helps us understand what the final answer is.

Why is this important? Well, the Hurwitz zeta function can tell us interesting things about numbers and how they behave when we do this special kind of adding up fractions. It's used in many areas of math, like number theory and calculus, to solve problems and explore the properties of different numbers.