Sum - 计蒜客

const int N = 20000005;

int n, tot;
int dp[N], p[N];

LL sum[N];
bool use[N];

void Inite() {
    dp[1] = sum[1] = 1;
    rep(i, 2, N) {
       if (!use[i]) {
            p[tot++] = i;
            dp[i] = 2;
       }
       for (int j = 0; j < tot && i * p[j] < N; ++j) {
            int tp = i * p[j];
            use[tp] = 1;
            if (i % p[j] == 0) {
                if ((i / p[j]) % p[j] == 0) dp[tp] = 0;
                else dp[tp] = dp[i] / 2;
                break;
            }
            dp[tp] = dp[i] * 2;
       }
    }
    rep(i, 2, N) sum[i] = sum[i - 1] + dp[i];
}

int main()
{
    Inite();
    BEGIN() {
        sc(n);
        pr(sum[n]);
    }
    return 0;
}