Sum of first n numbers

No.11434901 ViewReplyOriginalReport
1621952 = a(1)
How would I go about finding the sum of the first 5, or 50, or 95 numbers in that sequence? I'm not interested in exact numbers because that's easy and wolfram alpha can solve it in 5 secs. I'd like to know the sum equation for it. How do I come up with that?