Question

How to print the first 25 abundant odd numbers in C

Answer 1

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

// abundant odd number = sum of proper divisors > number

unsigned SumOddNumberProperDivisors(const unsigned num) {
    unsigned sum = 1;
    
    for (unsigned i = 3, j; i < sqrt(num) + 1; i += 2) 
        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 += 2) {
        if (SumOddNumberProperDivisors(num) > num) {
            printf("%u: %u\n", ++i, num);
        }
    }
           
    return 0;
}




/*
run:

1: 945
2: 1575
3: 2205
4: 2835
5: 3465
6: 4095
7: 4725
8: 5355
9: 5775
10: 5985
11: 6435
12: 6615
13: 6825
14: 7245
15: 7425
16: 7875
17: 8085
18: 8415
19: 8505
20: 8925
21: 9135
22: 9555
23: 9765
24: 10395
25: 11025

*/

 

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