Numbers in a Triangle: Curious Question

[stanek]

Assume we arrange numbers in a triage like this,
<font class="small">Code:</font><hr /><pre>
1
2 3
4 5 6
7 8 9 10
11 12 13 14 15
...
</pre><hr />

Is it possible to create a formula(s) to find where X lies in the triangle? ie x=9 is row 4 position 3(or 5)

I am curious as to how this is done. Ive searched google for numbered triangles and all that I can find is Pascals triangle, which isn't the same thing.

Is there a name for numbers arranged this way?

Right now I think that finding the row would be a function involving the square root and the column(positon) a mod function.

Any help in the right direction to figuring this out would be appreciated. Thanks