Harmonic Number

The $n$-th harmonic number $H_n$ is: ¹

$$H_n = 1 + \frac 1 2 + \frac 1 3 + ... + \frac 1 n = \sum_{k=1}^n \frac 1 k$$

In Haskell: ¹

harmonicNumber n = sum [ 1.0 / (fromIntegral k) | k <- [1..n] ]