Check if a number is Quartan 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 ; Driver Code ; Check if number is prime and of the form 16 * n + 1
< ? php function isPrime ( $ n ) { if ( $ n <= 1 ) return false ; if ( $ n <= 3 ) return true ; if ( $ n % 2 == 0 $ n % 3 == 0 ) return false ; for ( $ i = 5 ; $ i * $ i <= $ n ; $ i = $ i + 6 ) { if ( $ n % $ i == 0 || $ n % ( $ i + 2 ) == 0 ) { return false ; } } return true ; } $ n = 17 ; if ( isPrime ( $ n ) && ( $ n % 16 == 1 ) ) { echo " YES " ; } else { echo " NO " ; }