Euler's Constant
If we define
\[
\gamma_n = \left(\sum_{i=1}^n \frac{1}{i}\right) - \ln n
\]
then Euler's constant is given by
\[
\gamma = \lim_{n \to \infty} \gamma_n
\]
where \(\sum\) is the summation sign and \(\displaystyle{\lim_{n \to \infty}}\) is the limit of a sequence.