Question

How to print the first abundant odd number greater than one billion 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()
{
    unsigned num = 1000000001;

    for (;; num += 2) {
        if (SumOddNumberProperDivisors(num) > num) {
            break;
        }
    }

    printf("%u", num);

    return 0;
}




/*
run:

1000000575

*/

 

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