Grandi's series

Etymology
Named after Luigi Guido Grandi (1671-1742), Italian mathematician.

Proper noun

 * 1)  The divergent infinite series $$ \sum_{n=0}^\infty (-1)^n = 1 - 1 + 1 - 1 + \cdots .$$

Usage notes
Rigorous summation methods assign a value of 1/2 to Grandis's series. See