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For every natural n, 7^n - 1 is divisible by which number?
A6
B8
C5
D14
Answer & Solution
Correct answer: A. 6
For n = 1 it is 6, and 7^(k+1) - 1 = 7(7^k - 1) + 6 keeps divisibility by 6; 6 does not divide into 5, 8 or 14 for n = 1.
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