Observation

I just realised something interesting with the pascal's triangle:
the choose 2 diagonal is actually a list of all the triangular numbers(1, 3, 6, 10, 15...).Is there a particular reason why this is true? And why does it apply to only the choose 2 diagonal and not any of the other diagonals?

@perceptiveeagle (x choose 2) =x(x1)/2