The number (248 - 1) is exactly divisible by two numbers between 60 and 70. The numbers are :
Options:
A . 63 and 65
B . 63 and 67
C . 61 and 65
D . 65 and 67
Answer: Option A (248 - 1) = [(26)8 - 1] = (64)8 - 1 When n is even , (xn - an) is completely divisible by both (x - a) and (x + a) ∴ (648 - 18) is divisible by both (64 - 1) and (64 + 1) ⇒ (248 - 1) is divisible by both 63 and 65
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