Java (perfect numer)

其實好簡單，不過你要識咩叫perfect number。
一個perfect number既所有因數加埋必須等於它的兩倍。

6就係一個perfect number，因為 1 + 2 + 3 + 6 = 12 = 2 x 6。
28又係一個perfect number，因為 1 + 2 + 4 + 7 + 14 + 28 = 56 = 2 x 28。

數論裏已經證明，如果一個number係even perfect number，它必定能寫成2m-1(2m-1)

所以我們可以用下列數行Java程序寫出來。


/**　Program for searching perfect numbers　*/
public class Program {
　public static void main(String[] args) {
　　int power = 2;
　　for (int i = 0; i < 4; i++) {
　　　int nextPower = power * 2;
　　　System.out.println((nextPower - 1) * power);
　　　power = nextPower;
　　}
　}
}

頭四個perfect numbers係：

6
28
120
496
祝你好運。

2007-10-22 20:01:13 補充：
You are right, I will modify the program to fit the requirements.

2007-10-25 01:14:12 補充：
With limited space for updating, I will just describe the approach, which is simple. Replace i by primes[i] by a hard-coded prime number array [2,3,5,7] then we solved the problem.