What is this math term?

Factual Questions
1

I know that “factorial” means the **product ** of all the positive integers from 1 to a given number.

What is the term for the **sum **of those numbers?

Thanks.

2

The triangular numbers.

3

(From MathWorld)

4

Or just “the summation of all integers from 1 to n”

5

There is no standard term for the operation. The triangular numbers are the sequence of sums, but you can’t use it like “n triangle”.

6

Because you can just say n(n+1)/2, I doubt there’s ever been a need for another name. (As ultrafilter said, “triangular numbers” refers to the sequence, rather than the operation.)