The value is the analytic continuation of Riemann's Zeta function at the argument -1. https://en.wikipedia.org/wiki/Riemann_zeta_function https://en.wikipedia.

The value is the analytic continuation of Riemann's Zeta function at the argument -1. https://en.wikipedia.org/wiki/Riemann_zeta_function https://en.wikipedia.org/wiki/Riemann_zeta_function There are several methods to define finite sums for divergent series. See the wikipedia article for a comprehensive list: https://en.wikipedia.org/wiki/Divergent_series https://en.wikipedia.org/wiki/Divergent_series