What is this math term?

[panache45]

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.

[Giles]

The triangular numbers.

[Giles]

(From MathWorld) (http://mathworld.wolfram.com/TriangularNumber.html)

[TJdude825]

Or just "the summation of all integers from 1 to n"

[ultrafilter]

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".

[tim314]

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.)