# Definition:Harmonic Numbers

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## Definition

The harmonic numbers are denoted $H_n$ and are defined for positive integers $n$:

$\displaystyle \forall n \in \Z, n \ge 0: H_n = \sum_{k \mathop = 1}^n \frac 1 k$

From the definition of vacuous summation it is clear that $H_0 = 0$.

### General Harmonic Numbers

Let $r \in \R_{>0}$.

For $n \in \N_{> 0}$ the Harmonic numbers order $r$ are defined as follows:

$\displaystyle H_n^{\left({r}\right)} = \sum_{k \mathop = 1}^n \frac 1 {k^r}$

## Examples

### Harmonic Number $H_0$

$H_0 = 0$

### Harmonic Number $H_1$

$H_1 = 1$

### Harmonic Number $H_2$

$H_2 = \dfrac 3 2$

### Harmonic Number $H_{10000}$

To $15$ decimal places:

$H_{10000} \approx 9 \cdotp 78760 \, 60360 \, 44382 \, \ldots$

## Notation

There is no standard notation for this series.

The notations $h_n$, $S_n$ and $\psi \left({n + 1}\right) + \gamma$ can be found in the literature.

The notation given here is as advocated by Donald E. Knuth.

## Also see

• Results about harmonic numbers can be found here.