素因数分解 | アルゴリズムとデータ構造 | Aizu Online Judge http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=NTL_1_A&lang=jp

NTL_1_A.cpp

#include <iostream>
#include <cmath>
using namespace std;

int main(){
  int n;
  cin >> n;
  cout << n << ":";
  for (int i = 2; i <= sqrt(n); i++) {
    while (n % i == 0) {
      cout << " " << i;
      n /= i;
    }
  }
  if (n != 1) {
    cout << " " << n;
  }
  cout << endl;
  return 0;
}