Sphenic Number

Difficulty Level : Easy
Last Updated : 26 Jan, 2021

A Sphenic Number is a positive integer n which is product of exactly three distinct primes. The first few sphenic numbers are 30, 42, 66, 70, 78, 102, 105, 110, 114, …
Given a number n, determine whether it is a Sphenic Number or not.

Examples:

Input : 30
Output : Yes
Explanation : 30 is the smallest Sphenic number, 
           30 = 2 × 3 × 5 
           the product of the smallest three primes

Input : 60
Output : No
Explanation : 60 = 2² x 3 x 5
              has exactly 3 prime factors but
              is not a sphenic number

Sphenic number can be checked by fact that every sphenic number will have exactly 8 divisor SPHENIC NUMBER
So first We will try to find if the number is having exactly 8 divisors if not then simply answer is no.If there are exactly 8 divisors then we will confirm weather the first 3 digits after 1 are prime or not.
Eg. 30 (sphenic number)
30=p*q*r(i.e p,q and r are three distinct prime no and their product are 30)
the set of divisor is (1,2,3,5,6,10,15,30).

Below is the implementation of the idea.

C++

// C++ program to check whether a number is a
// Sphenic number or not
#include<bits/stdc++.h>
using namespace std;
//create a global array of size 10001;
bool arr[1001];
// This functions finds all primes smaller than 'limit' 
// using simple sieve of eratosthenes. 
void simpleSieve() 
{
    // initialize all entries of it as true. A value 
    // in mark[p] will finally be false if 'p' is Not 
    // a prime, else true.
    memset(arr,true,sizeof(arr));
 
    // One by one traverse all numbers so that their 
    // multiples can be marked as composite. 
    for(int p=2;p*p<1001;p++)
    {  
        // If p is not changed, then it is a prime
        if(arr[p])
        {// Update all multiples of p 
            for(int i=p*2;i<1001;i=i+p)
            arr[i]=false;
        }
    }
}
int find_sphene(int N)
{
    int arr1[8]={0};   //to store the 8 divisors
    int count=0;        //to count the number of divisor
    int j=0;
    for(int i=1;i<=N;i++)     
    {
        if(N%i==0 &&count<9)        
        {
            count++;
            arr1[j++]=i;
        }
    }
    //finally check if there re 8 divisor and all the numbers are distinct prime no return 1
    //else return 0
    if(count==8 && (arr[arr1[1]] && arr[arr1[2]] && arr[arr1[3]]))
    return 1;
    return 0;
}
 
// Driver program to test above function 
int main() 
{ 
    int n = 60; 
    simpleSieve();
    int ans=find_sphene(n);
    if(ans)
    cout<<"Yes";
    else
    cout<<"NO";
} 

Java

// Java program to check whether a number is a
// Sphenic number or not
import java.util.*;
 
class GFG
{
   
// create a global array of size 10001;
static boolean []arr = new boolean[1001];
   
// This functions finds all primes smaller than 'limit' 
// using simple sieve of eratosthenes. 
static void simpleSieve() 
{
    // initialize all entries of it as true. A value 
    // in mark[p] will finally be false if 'p' is Not 
    // a prime, else true.
    Arrays.fill(arr, true);
 
    // One by one traverse all numbers so that their 
    // multiples can be marked as composite. 
    for(int p = 2; p * p < 1001; p++)
    {
       
        // If p is not changed, then it is a prime
        if(arr[p])
        {
           
          // Update all multiples of p 
            for(int i = p * 2; i < 1001; i = i + p)
            arr[i] = false;
        }
    }
}
static int find_sphene(int N)
{
    int []arr1 = new int[8];   // to store the 8 divisors
    int count = 0;        // to count the number of divisor
    int j = 0;
    for(int i = 1; i <= N; i++)     
    {
        if(N % i == 0 && count < 8)        
        {
            count++;
            arr1[j++] = i;
             
        }
    }
   
    // finally check if there re 8 divisor and 
    // all the numbers are distinct prime no return 1
    // else return 0);
    if(count == 8 && (arr[arr1[1]] && arr[arr1[2]] && arr[arr1[3]]))
      return 1;
     
    return 0;
}
 
// Driver code
public static void main(String[] args) 
{ 
    int n = 60; 
    simpleSieve();
    int ans = find_sphene(n);
    if(ans == 1)
      System.out.print("Yes");
    else
      System.out.print("NO");
} 
}
 
// This code is contributed by aashish1995

Python3

# Python3 program to check whether a number 
# is a Sphenic number or not
 
# Create a global array of size 1001;
arr = [True] * (1001)
 
# This functions finds all primes smaller 
# than 'limit' using simple sieve of 
# eratosthenes.
def simpleSieve():
     
    # Initialize all entries of it as 
    # True. A value in mark[p] will 
    # finally be False if 'p' is Not
    # a prime, else True.
    k = 0
 
    # One by one traverse all numbers so 
    # that their multiples can be marked
    # as composite.
    for p in range(2, 1001):
        if (p * p > 1001):
            break
             
        # If p is not changed, then it is a prime
        if (arr[p]):
 
            # Update all multiples of p
            for k in range(p, 1001, k + p):
                arr[k] = False
         
def find_sphene(N):
     
    # To store the 8 divisors
    arr1 = [0] * (8) 
     
    # To count the number of divisor
    count = 0
    j = 0
     
    for i in range(1, N + 1):
        if (N % i == 0 and count < 8):
            count += 1
            arr1[j] = i
            j += 1
             
    # Finally check if there re 8 divisor and
    # all the numbers are distinct prime no return 1
    # else return 0);
    if (count == 8 and (arr[arr1[1]] and
       arr[arr1[2]] and arr[arr1[3]])):
        return 1;
 
    return 0;
 
# Driver code
if __name__ == '__main__':
     
    n = 60
    simpleSieve()
    ans = find_sphene(n)
     
    if (ans == 1):
        print("Yes")
    else:
        print("NO")
 
# This code is contributed by gauravrajput1

C#

// C# program to check whether a number 
// is a Sphenic number or not
using System;
 
class GFG{
   
// Create a global array of size 10001;
static bool []arr = new bool[1001];
   
// This functions finds all primes smaller than
// 'limit'. Using simple sieve of eratosthenes. 
static void simpleSieve() 
{
     
    // Initialize all entries of it as true. 
    // A value in mark[p] will finally be 
    // false if 'p' is Not a prime, else true.
    for(int i = 0;i<1001;i++)
        arr[i] = true;
         
    // One by one traverse all numbers so 
    // that their multiples can be marked 
    // as composite. 
    for(int p = 2; p * p < 1001; p++)
    {
         
        // If p is not changed, then it
        // is a prime
        if (arr[p])
        {
             
            // Update all multiples of p 
            for(int i = p * 2; i < 1001; i = i + p)
                arr[i] = false;
        }
    }
}
 
static int find_sphene(int N)
{
     
    // To store the 8 divisors
    int []arr1 = new int[8];   
     
    // To count the number of divisor
    int count = 0;        
    int j = 0;
     
    for(int i = 1; i <= N; i++)     
    {
        if (N % i == 0 && count < 8)        
        {
            count++;
            arr1[j++] = i;
        }
    }
   
    // Finally check if there re 8 divisor 
    // and all the numbers are distinct prime
    // no return 1 else return 0);
    if (count == 8 && (arr[arr1[1]] && 
      arr[arr1[2]] && arr[arr1[3]]))
        return 1;
     
    return 0;
}
 
// Driver code
public static void Main(String[] args) 
{ 
    int n = 60; 
    simpleSieve();
    int ans = find_sphene(n);
     
    if (ans == 1)
        Console.Write("Yes");
    else
        Console.Write("NO");
} 
}
 
// This code is contributed by aashish1995

Output:

NO

References:
1. OEIS
2. https://en.wikipedia.org/wiki/Sphenic_number

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