Question 973104
Find the following sum: 1+2+4+8+...+2^k-1
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Sum of a geometric series:: 
S(n) = a[r^n - 1]/[r-1]
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Your Problem::
a = 1, r = 2
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S(k) = [2^k -1]/1 = 2^k - 1
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Cheers,
Stan H.
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