Java: Check if a given number is circular prime or not

Last update on May 15 2025 13:10:41 (UTC/GMT +8 hours)

Check Circular Prime Number

Write a Java program to check if a given number is a circular prime or not.

Circular Prime : A circular prime is a prime number with the property that the number generated at each intermediate step when cyclically permuting its (base 10) digits will be prime.

For example, 1193 is a circular prime, since 1931, 9311 and 3119 all are also prime. A circular prime with at least two digits can only consist of combinations of the digits 1, 3, 7 or 9, because having 0, 2, 4, 6 or 8 as the last digit makes the number divisible by 2, and having 0 or 5 as the last digit makes it divisible by 5.

Test Data
Input a number: 35

Pictorial Presentation:

Sample Solution:

Java Code:

import java.util.Scanner;
public class Example17  {

       public static void main( String args[] ){ 
        int num; 
        Scanner sc = new Scanner( System.in ); 
        System.out.print("Input a number: "); 
        num = sc.nextInt(); 
        int num_of_digits = 0, divisor_part=1, circular_num = num; 
        boolean allPrime = true; 
        for( int i = num; i > 0; i /= 10 ){
            num_of_digits++;
            divisor_part *=10;
        }
        divisor_part /=10;
        do{
            circular_num = circulate_func( circular_num, divisor_part );
            if( !isPrime( circular_num ) ) allPrime=false;
        }while( circular_num != num );
        if( allPrime ) System.out.println("It is Circular Prime number." );
        else System.out.println("It is not a Circular Prime number." );
    }


	public static boolean isPrime( int n ){
        int factorCount = 0;
        if( n < 2 ) return false;
        else if( n == 2 ) return true;
        else if( n % 2 == 0 ) return false;
        else{
            int num = (int) Math.sqrt( n );
            for( int i = 3 ; i <= num; i+=2 ){
                if( n %i == 0 ){
                    return false;
                }
            }
        }
        return true;
    }
    public static int circulate_func( int n, int divisor_part ){
         if( n < 10 ) return n; 
         else return ( n % divisor_part ) * 10 + n / divisor_part; 
   } 
  
}

Sample Output:

Input a number: 35                                                                                            
It is not a Circular Prime number.

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Java program to generate all cyclic permutations of a number and check if every rotation is prime.
• Write a Java program to determine the circular prime property using iterative digit rotation and a prime sieve.
• Write a Java program to find circular primes in a given range using Java streams for filtering.
• Write a Java program to optimize circular prime checking by rejecting numbers with non-candidate digits early.

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