Approximate Size of Sum of Harmonic Series

Theorem
Let $H_n$ denote the sum of the harmonic series:
 * $H_n = \ds \sum_{k \mathop = 1}^n \frac 1 k$

Then $H_n$ can be approximated as follows:
 * $H_n \approx \ln n + \gamma + \dfrac 1 {2 n} - \dfrac 1 {12 n^2} + \dfrac 1 {120 n^4} - \epsilon$

where:
 * $\gamma$ denotes the Euler-Mascheroni constant: $\gamma \approx 0 \cdotp 57721 \, 56649 \, \ldots$
 * $0 < \epsilon < \dfrac 1 {252 n^6}$