Java: Check whether a number is a Keith Number or not

Last update on March 11 2025 11:10:03 (UTC/GMT +8 hours)

Check Keith Number

Write a Java program to check whether a number is a Keith Number or not.

In recreational mathematics, a Keith number or repfigit number (short for repetitive Fibonacci-like digit) is a number in the following integer sequence:
14, 19, 28, 47, 61, 75, 197, 742, 1104, 1537, 2208, 2580, 3684, 4788, 7385, 7647, 7909, 31331, 34285, 34348, 55604, 62662, 86935, 93993, 120284, 129106, 147640, 156146, 174680, 183186, 298320, 355419, 694280, 925993,

Test Data
Input a number: 75

Sample Solution:

Java Code:

import java.util.Scanner;
public class Example26  {

   public static void main(String[] args) { 

     Scanner sc = new Scanner( System.in ); 
     System.out.print("Input a number: "); 
     int n = sc.nextInt(); 
     int n1 = n;
     String s = Integer.toString(n);
     int d=s.length();
     int arr[]=new int[n];
     int i, sum; 
     for(i=d-1; i>=0; i--)
     {
         arr[i]=n1 % 10;
         n1=n1/10;
          
     }
      
     i=d; sum=0;
     while(sum<n)
     {
         sum = 0;
         for(int j=1; j<=d; j++)
         {
             sum=sum+arr[i-j];
         }
         arr[i]=sum;
         i++;
     }
 
    if(sum==n)
        System.out.println("Keith Number");
     else
        System.out.println("Not a Keith Number");
    }
}

Sample Output:

Input a number: 75                                                                                        
Keith Number 

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Java program to verify if a number is a Keith number by generating its digit sequence until the number is reached or exceeded.
• Write a Java program to generate all Keith numbers within a specified range using iterative loops.
• Write a Java program to implement a Keith number checker using a queue to simulate the digit sequence.
• Write a Java program to optimize Keith number detection by caching intermediate sequence sums.

Java Code Editor:

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