(sum 3i from i=0 to (999/3)) + (sum 5j from j=0 to (999/5)) - (sum 15k from k=0 to (999/15))

Uh oh! Wolfram|Alpha doesn't run without JavaScript.

Please enable JavaScript. If you don't know how, you can find instructionshere.Once you've done that, refresh this page to start using Wolfram|Alpha.