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Wow. Didn't know Wolfram could do that. Thanks.
Here's what it gave me:
\sum_{i=0}^{n} i/2^{-i} = 2^{-n}(-n+2^{n+1} -2)
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Oops. Yeah, that's what I meant.
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\sum_{i=1}^{n}[i/2^i]
Have looked and looked and cannot find it anywhere.
EDITED: To correct mistake.