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Project Euler: problem 3

Đề bài:

The prime factors of 13195 are 5, 7, 13 and 29.

What is the largest prime factor of the number 600851475143 ?

Tức là tìm ước số nguyên tố lớn nhất của 600851475413.

Bài này thì đương nhiên là quá dễ, tuy nhiên nếu viết bằng C++ thì cần chú ý là không thể sử dụng các kiểu cơ bản như long, vì sẽ bị tràn số.

Sử dụng kiểu long long int, và chú ý là thêm LL vào sau giá trị của biến có kiểu long long int.

Mã nguồn được viết và biên dịch bởi Code:Blocks 8.02, Windows XP.



bool check_prime (long long int a) {

    if (a==2) return true;

    for (long long int i = 2; i <= sqrt(a); i++) {

        if (a % i == 0) return false;


    return true;


int main() {

    long long int n = 600851475143LL;

    long long int s = long(sqrt(n));

    for (long long int i = s; i >= 2; i--) {

        if ((n % i == 0) && check_prime(i)) {

            cout <<>






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