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)
Solution Stats
Problem Comments
4 Comments
Solution Comments
Show comments
Loading...
Problem Recent Solvers759
Suggested Problems
-
4489 Solvers
-
528 Solvers
-
Deleting an element in a matrix
494 Solvers
-
6245 Solvers
-
Convert from Fahrenheit to Celsius
28279 Solvers
More from this Author43
Problem Tags
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
15 = 2*7+1 and 7 = 2*3+1 so 15 should be a safe prime. Am I missing something?
An (extra) safe prime number itself must be a prime number. Here, 15 is not a prime, so it is not (extra) safe prime
For case 8, x = 719;
which will lead to 44, not prime, the result should be false, but it's true now.
Am I right?
danteliujie, x = 719 does not lead to 44.