1 − 1 + 2 − 6 + 24 − 120 + ⋯

To evaluate the series \( S = 1 - 1 + 2 - 6 + 24 - 120 + \cdots \), we can identify the terms in the series in a more systematic way. We observe that the series can be expressed in terms of factorials: - The \( n \)-th term appears to follow the pattern \( (-1)^n n! \).