Monday-Saturday Prime Factors

http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=1154

001 #include<iostream>
002 using namespace std;
003 #define MAX 300001
004 
005 bool prime[MAX];
006 
007 void generate(){
008     fill( prime, prime + MAX, false ) ;
009     for ( int i = 1, k = 0; i <= MAX; k++){
010         prime[i] = true;
011         i += ((k % 2 == 0) ? 5 : 2);
012     }
013     prime[1] = false;
014     for ( int i = 1, k = 0; i * i <= MAX; k++ ){
015         if ( prime[i] ) {
016             for ( int j = 2*i; j <= MAX; j += i ) prime[j] = false;
017         }
018         i += ((k % 2 == 0) ? 5 : 2);
019     }
020 }
021 
022 main(){
023     generate();
024     int x;
025     while( cin >> x ){
026         if ( x == 1 ) break;
027         cout << x << ":";
028         for ( int i = 1; i <= MAX; i++ ){
029             if ( prime[i] && x % i == 0 ) cout << " " << i;
030         }
031         cout << endl;
032     }
033 }