 Grandi's series is recovered by letting "z" = 0.Unlike the geometric series, the Dirichlet series for "η" is not useful for determining what 1 − 1 + 1 − 1 + · · · "should" be.Even on the right half-plane, "η"("z") is not given by any elementary expression, and there is no immediate evidence of its limit as "z" approaches 0.