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Which of the following exactly divides $(1 7^{200} - 1)$ ?

Competition practiceNumber System, HCF & LCM

A19
B7
C18
D13

Step-by-Step Solution

For even

n, x^{n} - a^{n}

is divisible by both

x - a

and

x + a

. So

1 7^{200} - 1

is divisible by

17 + 1 = 18

.

Answer: C) 18

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