自守数，亲密数，完美数

自守数:

 

public class AutomorphicNum{public static void main(String[] args){for(int i=1;i<=999;i++)judge(i);}public static void judge(long n){ int bit = getBit(n); long mod = (long) Math.pow(10, bit); if(((n*n-n)%mod)==0) System.out.println(n*n+" "+n);}private static int getBit(long n) {int bit = 0;while(n!=0){n=n/10;bit++;}return bit;}}

 

亲密数

public class FriendNum {public static void main(String[] args){int count1=0;int count2=0;int[] fac1;int[] fac2;int sum1 ;int sum2 ;for(int num=1;num<10000;num++){sum1 = 0;sum2 = 0;count1 = 0;count2 = 0;fac1 = new int[100];fac2 = new int[100];for(int i=1;i<=num/2;i++){if(num%i==0){fac1[count1++] = i;sum1+=i;}}for(int i=1;i<=sum1/2;i++){if(sum1%i==0){fac2[count2++] = i;sum2+=i;}}if(sum2==num&&num>sum1){ System.out.print(sum1+" = "); for(int i=0;i<count1-1;i++) System.out.print(fac1[i]+" + "); System.out.print(fac1[count1-1]); System.out.print("/t"); System.out.print(num+" = "); for(int i=0;i<count2-1;i++) System.out.print(fac2[i]+" + "); System.out.println(fac2[count2-1]);}}}}

 

完美数

public class PerfectNum {public static void main(String[] args){int[] factor = new int[500];int count = 0;int sum;for(int num=1;num<=100000;num++){count = 0;sum = num;for(int i=1;i<=num/2;i++){if(num%i==0){sum -=i;factor[count++] = i;}}if(sum==0){System.out.print(num+ " = ");for(int j=0;j<count-1;j++){System.out.print(factor[j]+" + ");}System.out.println(factor[count-1]);}}}}