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Primality test for the sum of digits at odd places of a number
  • Last Updated : 26 Apr, 2021

Given an integer ‘n’, the task is to check whether the sum of digits at the odd positions (from right to left) is prime or not. 
If it is prime then, print “YES” or “NO” otherwise.
Examples: 
 

Input: n = 123 
Output: NO 
As, 1 + 3 = 4 is not prime.
Input: n = 42 
Output: YES 
Since, 2 is a prime. 
 

 

Approach: First, find the sum of the digits which are at odd positions i.e, 1, 3, 5, … (starting from right). 
If the sum is prime then print ‘YES’ else print ‘NO’.
Below is the implementation of the above approach: 
 

C++




// C++ program to do Primality test
// for the sum of digits at
// odd places of a number
 
#include <bits/stdc++.h>
using namespace std;
 
// Function that return sum
// of the digits at odd places
int sum_odd(int n)
{
    int sum = 0, pos = 1;
    while (n) {
        if (pos % 2 == 1)
            sum += n % 10;
        n = n / 10;
        pos++;
    }
    return sum;
}
 
// Function that returns true
// if the number is prime
// else false
bool check_prime(int n)
{
    // Corner cases
    if (n <= 1)
        return false;
    if (n <= 3)
        return true;
 
    // This condition is checked so that
    // we can skip middle five
    // numbers in the below loop
    if (n % 2 == 0 || n % 3 == 0)
        return false;
 
    for (int i = 5; i * i <= n; i = i + 6)
        if (n % i == 0 || n % (i + 2) == 0)
            return false;
 
    return true;
}
 
// Driver code
int main()
{
    int n = 223;
 
    // Get the sum of the
    // digits at odd places
    int sum = sum_odd(n);
 
    if (check_prime(sum))
        cout << "YES" << endl;
    else
        cout << "NO" << endl;
    return 0;
}

Java




// Java  program to do Primality test
// for the sum of digits at
// odd places of a number
 
import java.io.*;
 
class GFG {
    // Function that return sum
// of the digits at odd places
static int sum_odd(int n)
{
    int sum = 0, pos = 1;
    while (n>0) {
        if (pos % 2 == 1)
            sum += n % 10;
        n = n / 10;
        pos++;
    }
    return sum;
}
 
// Function that returns true
// if the number is prime
// else false
static boolean check_prime(int n)
{
    // Corner cases
    if (n <= 1)
        return false;
    if (n <= 3)
        return true;
 
    // This condition is checked so that
    // we can skip middle five
    // numbers in the below loop
    if (n % 2 == 0 || n % 3 == 0)
        return false;
 
    for (int i = 5; i * i <= n; i = i + 6)
        if (n % i == 0 || n % (i + 2) == 0)
            return false;
 
    return true;
}
 
// Driver code
    public static void main (String[] args) {
     
    int n = 223;
    // Get the sum of the
    // digits at odd places
    int sum = sum_odd(n);
    if (check_prime(sum))
        System.out.println ("YES" );
    else
        System.out.println("NO");
    }
}

Python3




# Python3 program to do Primality test 
# for the sum of digits at 
# odd places of a number
 
# Function that return sum
# of the digits at odd places
def sum_odd(n):
    sums = 0
    pos = 1
    while (n!=0):
        if (pos % 2 == 1):
            sums += n % 10
        n = n // 10
        pos+=1
    return sums
 
# Function to check if a
# number is prime
 
def check_prime(n):
    # Corner cases
    if (n <= 1):
        return False
    if (n <= 3):
        return True
   
     # This is checked so that we can skip
     # middle five numbers in below loop
    if (n % 2 == 0 or n % 3 == 0):
        return False
   
    for i in range(5,n,6):
        if (n % i == 0 or n % (i + 2) == 0):
            return False
    return True
 
#driver code
n = 223
# Get the sum of the
# digits at odd places
sums = sum_odd(n)
if (check_prime(sums)):
    print("YES")
else:
    print("NO")
 
#this code is improved by sahilshelangia

C#




// C#  program to do Primality test
// for the sum of digits at
// odd places of a number
using System;
 
public class GFG{
     
// Function that return sum
// of the digits at odd places
static int sum_odd(int n)
{
    int sum = 0, pos = 1;
    while (n>0) {
        if (pos % 2 == 1)
            sum += n % 10;
        n = n / 10;
        pos++;
    }
    return sum;
}
 
// Function that returns true
// if the number is prime
// else false
static bool check_prime(int n)
{
    // Corner cases
    if (n <= 1)
        return false;
    if (n <= 3)
        return true;
 
    // This condition is checked so that
    // we can skip middle five
    // numbers in the below loop
    if (n % 2 == 0 || n % 3 == 0)
        return false;
 
    for (int i = 5; i * i <= n; i = i + 6)
        if (n % i == 0 || n % (i + 2) == 0)
            return false;
 
    return true;
}
 
// Driver code
     
    static public void Main (){
        int n = 223;
    // Get the sum of the
    // digits at odd places
    int sum = sum_odd(n);
    if (check_prime(sum))
        Console.WriteLine("YES" );
    else
            Console.WriteLine("NO");
    }
}

PHP




<?php
// PHP program to do Primality test
// for the sum of digits at odd
// places of a number
 
// Function that return sum
// of the digits at odd places
function sum_odd($n)
{
    $sum = 0;
    $pos = 1;
    while ($n)
    {
        if ($pos % 2 == 1)
            $sum += $n % 10;
        $n = (int)($n / 10);
        $pos++;
    }
    return $sum;
}
 
// Function that returns true
// if the number is prime
// else false
function check_prime($n)
{
    // Corner cases
    if ($n <= 1)
        return false;
    if ($n <= 3)
        return true;
 
    // This condition is checked so
    // that we can skip middle five
    // numbers in the below loop
    if ($n % 2 == 0 || $n % 3 == 0)
        return false;
 
    for ($i = 5; $i * $i <= $n;
                 $i = ($i + 6))
        if ($n % $i == 0 ||
            $n % ($i + 2) == 0)
            return false;
 
    return true;
}
 
// Driver code
$n = 223;
 
// Get the sum of the
// digits at odd places
$sum = sum_odd($n);
 
if (check_prime($sum))
    echo "YES";
else
    echo "NO";
 
// This code is contributed by ajit
?>

Javascript




<script>
 
// JavaScript program to do Primality test
// for the sum of digits at
// odd places of a number
 
 
// Function that return sum
// of the digits at odd places
function sum_odd(n)
{
    let sum = 0, pos = 1;
    while (n) {
        if (pos % 2 == 1)
            sum += n % 10;
        n = Math.floor(n / 10);
        pos++;
    }
    return sum;
}
 
// Function that returns true
// if the number is prime
// else false
function check_prime(n)
{
    // Corner cases
    if (n <= 1)
        return false;
    if (n <= 3)
        return true;
 
    // This condition is checked so that
    // we can skip middle five
    // numbers in the below loop
    if (n % 2 == 0 || n % 3 == 0)
        return false;
 
    for (let i = 5; i * i <= n; i = i + 6)
        if (n % i == 0 || n % (i + 2) == 0)
            return false;
 
    return true;
}
 
// Driver code
 
    let n = 223;
 
    // Get the sum of the
    // digits at odd places
    let sum = sum_odd(n);
 
    if (check_prime(sum))
        document.write("YES" + "<br>");
    else
        document.write("NO" + "<br>");
 
// This code is contributed by Surbhi Tyagi.
 
</script>
Output: 
YES

 

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