Print all Semi-Prime Numbers less than or equal to N in C++

In this problem, we are given an integer N. and we have to print all the semiprime numbers that are less than or equal to N.

Before solving this problem, let’s understand what is a semi-prime number.

A semi-prime number is a number whose value is the product of two distinct prime numbers.

Let’s take an example,

21 = 3*7 is a semiprime number.

25 = 5*5 is not a semiprime number.

Now, let’s take an example of semiprime numbers less than or equal to n.

Input: N = 15
Output: 6 10 14 15

To solve this problem, we have to take each number less than equal to N and check if it has exactly two distinct prime factors.

Tip − we can also start our algorithm from 6 as the smallest semi-prime number is 6.

Example

 Live Demo

#include <bits/stdc++.h>
using namespace std;
vector<int>generateSemiPrimeNumbers(int n){
   int index[n + 1];
   for (int i = 1; i <= n; i++)
      index[i] = i;
   int countDivision[n + 1];
   for (int i = 0; i < n + 1; i++)
      countDivision[i] = 2;
   for (int i = 2; i <= n; i++) {
      if (index[i] == i && countDivision[i] == 2) {
         for (int j = 2 * i; j <= n; j += i) {
            if (countDivision[j] > 0) {
               index[j] = index[j] / i;
               countDivision[j]--;
            }
         }
      }
   }
   vector<int> semiPrime;
   for (int i = 2; i <= n; i++) {
      if (index[i] == 1 && countDivision[i] == 0) semiPrime.push_back(i);
   }
   return semiPrime;
}
int main(){
   int n = 15;
   cout<<"Semi-prime numbers less that or equal to "<<n<<"are :\n";
   vector<int>semiPrime = generateSemiPrimeNumbers(n);
   for (int i = 0; i < semiPrime.size(); i++)
      cout<<semiPrime[i]<<"\t";
   return 0;
}

Output

Semi-prime numbers less than or equal to 15 are −

6 10 14 15

Sudhir sharma

Published on 17-Jan-2020 11:01:15

• Related Questions & Answers
• Print all prime numbers less than or equal to N in C++
• Find all factorial numbers less than or equal to n in C++
• Find maximum product of digits among numbers less than or equal to N in C++
• Print all numbers less than N with at-most 2 unique digits in C++
• Print all Prime Quadruplet of a number less than it in C++
• Count all the numbers less than 10^6 whose minimum prime factor is N C++
• Nearest prime less than given number n C++
• Print all Jumping Numbers smaller than or equal to a given value in C++
• Recursive program to print all numbers less than N which consist of digits 1 or 3 only in C++
• Print triplets with sum less than or equal to k in C Program
• Find Multiples of 2 or 3 or 5 less than or equal to N in C++
• Find Largest Special Prime which is less than or equal to a given number in C++
• An interesting solution to get all prime numbers smaller than n?
• Find unique pairs such that each element is less than or equal to N in C++
• Minimum swaps required to bring all elements less than or equal to k together in C++