Euler Project #12

12.c

#include<stdio.h>
static long get_factor_num(long n) {
    int factor;
    int exp_count = 0;
    int ans = 1;
    for (factor = 2; n > 1; factor++) {
        exp_count = 0;
        while (n % factor == 0) {
            n /= factor;
            ++exp_count;
        }
        ans *= (exp_count + 1);
    }
    return ans;
}
int main() {
    long n;
    long num_factor_last = 0, num_factor_now;
    for (n = 2; ; n++) {
        if (n % 2) {
            num_factor_now = get_factor_num(n);
        } else {
            num_factor_now = get_factor_num(n / 2);
        }
        if (num_factor_last * num_factor_now > 500) {
            break;
        }
        num_factor_last = num_factor_now;
    }
    printf("%ld\n", n * (n-1) / 2);
}