Untouchable Numbers.java

Author: geekboi777

Untouchable Numbers/Untouchable Numbers.java

@@ -0,0 +1,62 @@
+import java.util.*;
+// Java program for the above approach
+class Main{
+ 
+// Function to calculate sum of
+// all proper divisors of num
+static int divSum(int num)
+{
+ 
+    // Final result of summation
+    // of divisors
+    int result = 0;
+ 
+    // Find all divisors of num
+    for(int i = 2; i <= Math.sqrt(num); i++)
+    {
+        
+       // If 'i' is divisor of 'num'
+       if (num % i == 0)
+       {
+            
+           // If both divisors are same
+           // then add it only once else
+           // add both
+           if (i == (num / i))
+               result += i;
+           else
+               result += (i + num / i);
+       }
+    }
+     
+    // Add 1 to the result as
+    // 1 is also a divisor
+    return (result + 1);
+}
+ 
+// Function to check if N is a
+// Untouchable Number
+static boolean isUntouchable(int n)
+{
+    for(int i = 1; i <= 2 * n; i++)
+    {
+       if (divSum(i) == n)
+           return false;
+    }
+    return true;
+}
+ 
+// Driver code
+public static void main(String[] args)
+{
+ 
+    // Given Number N
+    int n;
+    Scanner sc = new Scanner(System.in);
+    n = sc.nextInt();
+    // Function Call
+    for (int i =0 ; i<=n; i++)
+        if (isUntouchable(i))
+            System.out.print(i+" ");
+}
+}