A prime number is called a "Superprime" if doubling it, and then subtracting 1 , results in another prime number. The number of Superprimes less than 15 is
(A) 2
(B) 3
(C) 4
(D) 5
(E) 6
A prime number is called a "Superprime" if doubling it, and then subtracting 1 , results in another prime number. The number of Superprimes less than 15 is
(A) 2
(B) 3
(C) 4
(D) 5
(E) 6

## Solution

The only possible candidates for 'Superprimes' are 2, 3, 5, 7, 11 and 13 since they are the only prime numbers less than 15 . If we double each of these numbers and then subtract 1 we get $3,5,9,13,21$ and 25. Three of these results are prime numbers. So there are only three Superprimes.

ANswer: (B)