[alexchamberlain]

Python 2.7 can do it in 0.0867 usec (Intel i7);

    $ python2.7 -m timeit 'n=10**9; (n*n + n) / 2'
    10000000 loops, best of 3: 0.0867 usec per loop

(Admittedly, I killed `n=109; sum(range(1,n+1))`.)