Question

How to print the first 25 abundant numbers in C

Answer 1

#include <stdio.h>
#include <math.h>

// abundant number = sum of proper divisors > number

unsigned SumNumberProperDivisors(const unsigned num) {
    unsigned sum = 1;
    
    for (unsigned i = 2, j; i * i <= num; i++)
        if (num % i == 0)
            sum += i + (i == (j = num / i) ? 0 : j);
    
    return sum;
}
    
int main()
{
    for (unsigned num = 1, i = 0; i < 25; num++) {
        if (SumNumberProperDivisors(num) > num) {
            printf("%u: %u\n", ++i, num);
        }
    }
           
    return 0;
}






/*
run:

1: 12
2: 18
3: 20
4: 24
5: 30
6: 36
7: 40
8: 42
9: 48
10: 54
11: 56
12: 60
13: 66
14: 70
15: 72
16: 78
17: 80
18: 84
19: 88
20: 90
21: 96
22: 100
23: 102
24: 104
25: 108

*/

 

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Answer 2

#include <stdio.h>

// abundant number = sum of proper divisors > number

unsigned SumNumberProperDivisors(const unsigned num) {
    unsigned sum = 0;

    for (unsigned i = 2, j; i * i <= num; i++) {
        if (num % i == 0) {
            sum += i;
            if (num / i != i) {
                sum += num / i;
            }
        }
    }
    
    return sum;
}

int main()
{
    for (unsigned num = 1, i = 0; i < 25; num++) {
        if (SumNumberProperDivisors(num) > num) {
            printf("%u: %u\n", ++i, num);
        }
    }

    return 0;
}




/*
run:

1: 12
2: 18
3: 20
4: 24
5: 30
6: 36
7: 40
8: 42
9: 48
10: 54
11: 56
12: 60
13: 66
14: 70
15: 72
16: 78
17: 80
18: 84
19: 88
20: 90
21: 96
22: 100
23: 102
24: 104
25: 108

*/

 

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