Does this help?

sum n(21-n) from n=1 through 20 - Wolfram|Alpha

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- Apr 28th 2013, 12:20 PM #1

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- Apr 28th 2013, 12:50 PM #2
## Re: SUM

Does this help?

sum n(21-n) from n=1 through 20 - Wolfram|Alpha

- Apr 28th 2013, 12:50 PM #3