Sigma calculation in efficient way

sigma_calculation_efficient.cpp

#include <iostream>
#include <vector>
#include <math.h>

using namespace std;

#define READ(x) freopen(x, "r", stdin)
#define WRITE(x) freopen(x, "w", stdout)

#define PB push_back

typedef unsigned long long ULL;
typedef vector<int> VI;

#define MAX_PRIME 10000000
#define MAX 10000000

uint bigPrime[MAX + 7];
uint t[MAX + 7];
ULL sigma[MAX + 7];

void preCal() {
    t[1] = sigma[1] = 1;

    int root = (uint)sqrt(MAX);
    memset(bigPrime, 0, sizeof(bigPrime));
    for (int i = 2; i <= MAX; ++i) {
        if (bigPrime[i] == 0) {
            bigPrime[i] = i;
            if (i > root) continue;
            for (int j = i*i; j <= MAX; j += i) {
                bigPrime[j] = i;
            }
        }
    }

    for (int i = 2; i <= MAX; ++i) {
        int p = bigPrime[i];
        int a = 0;
        int pa = p;
        int tmp = i;
        while (tmp % p == 0) {
            tmp /= p;
            a = a + 1;
            pa = pa * p;
        }
        t[i] = (a + 1) * t[tmp];
        sigma[i] = (pa - 1) / (p - 1) * sigma[tmp];
    }
}

int main() {
    WRITE("output.txt");

    double cl = clock();

    preCal();

    for (int i = 1; i <= 30; ++i) {
        printf("%d: %lu %llu\n", i, t[i], sigma[i]);
    }

    cl = clock() - cl;
    fprintf(stderr, "Total Execution Time = %lf seconds\n", cl / CLOCKS_PER_SEC);
}