Problem 44385. Extra safe primes

Did you know that the number 5 is the first safe prime? A safe prime is a prime number that can be expressed as 2p+1, where p is also a prime.

To celebrate Cody's Five-Year Anniversary, write a function to determine if a positive integer n is a safe prime in which the prime p (such that n=2p+1) is also a safe prime.

Examples

isextrasafe(5) = false % because 5=2*2+1 and 2 is not a safe prime
isextrasafe(23) = true % because 23=2*11+1 and 11 is also a safe prime (11=2*5+1)