Sophie Germain Prime | function to detect prime number here we have used sieve method https : www . geeksforgeeks . org / sieve - of - eratosthenes / to detect prime number ; If prime [ p ] is not changed , then it is a prime ; Update all multiples of p ; We have made array till 2 * n + 1 so that we can check prime number till that and conclude about sophie german prime . ; checking every i whether it is sophie german prime or not . ; Driver code
< ? php function sieve ( $ n , & $ prime ) { for ( $ p = 2 ; $ p * $ p <= $ n ; $ p ++ ) { if ( $ prime [ $ p ] == true ) { for ( $ i = $ p * 2 ; $ i <= $ n ; $ i += $ p ) $ prime [ $ i ] = false ; } } } function printSophieGermanNumber ( $ n ) { $ prime = array ( ) ; for ( $ i = 0 ; $ i < ( 2 * $ n + 1 ) ; $ i ++ ) $ prime [ $ i ] = true ; sieve ( 2 * $ n + 1 , $ prime ) ; for ( $ i = 2 ; $ i <= $ n ; ++ $ i ) { if ( $ prime [ $ i ] && $ prime [ 2 * $ i + 1 ] ) echo ( $ i . " ▁ " ) ; } } $ n = 25 ; printSophieGermanNumber ( $ n ) ; ? >