1 − 2 + 3 − 4 + ⋯

In mathematics, $1-2+3-4+···$ is an infinite series whose terms are the successive positive integers, given alternating signs.

Using sigma summation notation the sum of the first m terms of the series can be expressed as

${\displaystyle \sum _{n=1}^{m}n(-1{)}^{n-1}.}$

Read more »