Composite Numbers

The following programs will find if a number is composite or not and will print a series of composite numbers.
A composite number is a positive integer that has a positive divisor other than one or itself. In other words a composite number is any positive integer greater than one that is not a prime number.

So, if n > 0 is an integer and there are integers 1 < a, b < n such that n = a × b, then n is composite. By definition, every integer greater than one is either a prime number or a composite number. The number one is a unit – it is neither prime nor composite. For example, the integer 14 is a composite number because it can be factored as 2 × 7. Likewise, the integers 2 and 3 are not composite numbers because each of them can only be divided by one and itself.

The first 105 composite numbers are

4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 25, 26, 27, 28, 30, 32, 33, 34, 35, 36, 38, 39, 40, 42, 44, 45, 46, 48, 49, 50, 51, 52, 54, 55, 56, 57, 58, 60, 62, 63, 64, 65, 66, 68, 69, 70, 72, 74, 75, 76, 77, 78, 80, 81, 82, 84, 85, 86, 87, 88, 90, 91, 92, 93, 94, 95, 96, 98, 99, 100, 102, 104, 105, 106, 108, 110, 111, 112, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 128, 129, 130, 132, 133, 134, 135, 136, 138, 140.

/*checks if it is a composite number or not i.e. has factor other than 1 and itself*/


#include<stdio.h>
int main()
{
    int i,n,factor;
    printf("Enter the number:");
    scanf("%d",&n);
    for(i=1;i<n;i++)
    {
         if(n%i==0) 
         {
             factor=i;/*finds the largest proper divisor*/
         }
    }
    if(factor>1) 
    {
          printf ("The number is a composite number!");
    }
    else 
    {
          printf ("This is not a composite number!");
    }
    return 0;
}

input:21
output:The number is a composite number!

input:23
output:This is not a composite number!

Now we will use the above logic to print a series of composite number

/*prints a series of composite numbers*/

#include<stdio.h>
int main()
{
    int i,n,factor;
    printf("Enter the last number of the sequence:");
    scanf("%d",&j);
    for(n=2;n<=j;n++)
    {
         for(i=1;i<n;i++)
         {
              if(n%i==0) 
              {
                   factor=i;/*finds the largest proper divisor*/
              }
         }
         if(factor>1) 
         {
              printf ("%d",n);
         }              
     }
     return 0;
}

compiled on:gcc and linux
input:100
output:4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 25, 26, 27, 28, 30, 32, 33, 34, 35, 36, 38, 39, 40, 42, 44, 45, 46, 48, 49, 50, 51, 52, 54, 55, 56, 57, 58, 60, 62, 63, 64, 65, 66, 68, 69, 70, 72, 74, 75, 76, 77, 78, 80, 81, 82, 84, 85, 86, 87, 88, 90, 91, 92, 93, 94, 95, 96, 98, 99