Good ole' Gauss
http://mathforum.org/library/drmath/view/57919.html

1 plus N quantity times N divided by 2.

so 

sum 1..100001 == 5000150001
#and
(100001+1)*(100001/2) == 5000150001

[download]
Doesn't help much in this, but is interesting nonetheless.

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In reply to Re: Math fun. by suaveant
in thread Math fun. by BrowserUk

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