The formula for the sum of an arithmetic series is given by:
\[ S = \frac{n}{2}(a_1 + a_n) \]
where:
- \( S \) is the sum of the series,
- \( n \) is the number of terms in the series,
- \( a_1 \) is the first term of the series, and
- \( a_n \) is the last
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