text: Check whether the given number is Wagstaff prime or not | Function to check if a number is prime or not ; Corner cases ; This is checked so that we can skip middle five numbers in below loop ; Utility function to check power of two ; Driver Code ; Check if number is prime and of the form ( 2 ^ q + 1 ) / 3
code: < ? php function isPrime ( $ n ) { if ( $ n <= 1 ) return false ; if ( $ n <= 3 ) return true ; if ( $ n % 2 == 0 or $ n % 3 == 0 ) return false ; for ( $ i = 5 ; $ i * $ i <= $ n ; $ i = $ i + 6 ) { if ( $ n % $ i == 0 or $ n % ( $ i + 2 ) == 0 ) { return false ; } } return true ; } function isPowerOfTwo ( $ n ) { return ( $ n && ! ( $ n & ( $ n - 1 ) ) ) ; } $ n = 43 ; if ( isPrime ( $ n ) && ( isPowerOfTwo ( $ n * 3 - 1 ) ) ) { echo " YES " ; } else { echo " NO " ; } ? >