That's not entirely right. It should be: print ((n+1)*n)/2

(fold the sequence in half, which gives you 100 + 1 on one end and 50 + 51 on the other.)

Ah right, sure.

I took the 'n' to be the 100, not the 101. A little too quick on the submit there, I should have run it :)

But anyway, that seems to be a damn sight faster than to run a loop to add a bunch of numbers in a fixed interval.

Especially for large 'n'.

Probably much faster, but also doing half the work yourself. It'll depend on the situation which is the better solution.