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The smallest positive prime (say p) such that 2 p - 1is not a prime is

5
11
17
29

Correct Answer: 11

Explanation:

Taking p = 11
2^p - 1 = 2¹¹ - 1
= 2047
Since 2047 is divisible by 23 it is not prime. Thus, required least positive prime number is 11.

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