## Series of zeta sum

Let denote the Riemann zeta function. Evaluate the series:

**Solution**

Let . We are proving the more general result.

where denotes the digamma function.

First of all, we note that:

Thus,

due to the reflection formula .

**Side note: **If then the sum equals .

## Lebesgue measure of Cantor set

An alternative way to define the Cantor set is the following:

What is the Lebesgue measure of the Cantor set if we consider it as a subset of ? Is countable?

## A divergent series …. or maybe not?

The number ranges over all possible powers with both the base and the exponent positive integers greater than , assuming each such value only once. Prove that:

Let us denote by the set of positive integers greater than that are not perfect powers ( i.e are not of the form , where is a positive integer and ). Since the terms of the series are positive , we can freely permute them. Thus,

## Iterated exponential integral

Prove that

**Solution**

We begin by stating a lemma:

**Lemma: **Let be an analytic function on some closed disk which has center and radius . Let denote the the boundary of the disk. It holds that

*Proof:* By the Cauchy integral formula we have that

The equation of a circle of radius and centre is given by . Hence,

and the proof is complete.

* Something quickie: *Given the assumptions in Gauss’ MVT, we have

The proof of the result is pretty straight forward by using the fact that

Back to the problem the result now follows by the lemma.