Sum of the first n numbers

Legend says Gauss found 1 + 2 + … + 100 = 5050 as a schoolboy by pairing 1 with 100, 2 with 99, and so on. History: traditionally 1780s.

1 + 2 + \cdots + n = \frac{n(n+1)}{2}

How to work it out

1
The statement:
$1 + 2 + \cdots + n = \frac{n(n+1)}{2}$
2
Legend says Gauss found 1 + 2 + … + 100 = 5050 as a schoolboy by pairing 1 with 100, 2 with 99, and so on.
3
Below, the numbers in the table are computed by this site from the definition, not copied.

LaTeX source of the formulas on this page

\[ 1 + 2 + \cdots + n = \frac{n(n+1)}{2} \]

What is the sum of the first n numbers?

Legend says Gauss found 1 + 2 + … + 100 = 5050 as a schoolboy by pairing 1 with 100, 2 with 99, and so on.

Who is the Sum of the first n numbers associated with?

Carl Friedrich Gauss.