square sum.

gistfile1.txt

typedef long long int LLI;
#define SZ(x) int(x.size())
#define FOR(x,y,z) for(int x = y; y < z; x++)
#define REP(x,y) FOR(x,0,y)

int main(int argc, char *argv[]){
  vector<bool> v(30000000,false);

  FOR(i,1,3000){
    LLI n = i * i;
    FOR(j,i,3000){
      v[n + j*j] = true;
    }
  }
  int j = 0;
  REP(i,SZ(v)){
    if(v[i]) j++;
    if(j == 1000000){
      cout << i << endl;
      return 0;
    }
  }
  return 0;
}

$ time ./a.out

4917092
./a.out 0.02s user 0.02s system 84% cpu 0.048 total