# What is an intuitive way to see why harmonic series sums to logn?

So far the answers here have used calculus. However, you asked for an "intuitive" explanation, and it is likely that calculus is not intuitive to you, much less the evaluation of that particular integral.
I will give a very elementary argument for why $\sum_{k=1}^n \frac {1}{k} = \Theta (\log n)$.
Consider the following: $1 + 1/2 + 1/3 + 1/4 + 1/5 + 1/6 + 1/7 + … + 1/n \leq 1 + 1/2 + 1/2 + 1/4 + 1/4 + 1/4 + 1/4 + …+ 1/n =$$1 + 2 \times 1/2 + 4 \times 1/4 + … + n \times 1/n$. It takes $\log_2 n$ multiplies by 2 to reach n, and each summand in the final sequence equals 1.
So, $\sum_{k=1}^n \frac {1}{k} \leq \lceil \log_2 n \rceil + 1$.
We can also obtain a lower bound by rounding to powers of two in a different direction:
$1 + 1/2 + 1/3 + 1/4 + 1/5 + 1/6 + 1/7 + 1/8 + … + 1/n$$\geq 1 + 1/2 + 1/4 + 1/4 + 1/8 + 1/8 + 1/8 + 1/8 + …+ 1/n.$ Here each group of identical powers of two is worth 1/2, and then there's the 1. So here we get $1 + \frac {1}{2} \lfloor \log_2 n \rfloor$.
Therefore, the sum is $\Theta (\log n)$.

What is an intuitive way to see why harmonic series sums to logn?