CF 915 G WA

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <ctime>
#include <cmath>
#include <cassert>
#include <algorithm>
#include <vector>

#define max_v 2100000
#define int_max 0x3f3f3f3f
#define cont continue
#define pow_2(n) (1 << (n))
#define ll long long
#define pii pair<int, int>
#define pb push_back
#define mp make_pair
#define lsb(n) ((n)&(-(n)))
#define LC(n) (((n) << 1) + 1)
#define RC(n) (((n) << 1) + 2)
#define add(a, b) (((a)%mod + (b)%mod)%mod)
#define mul(a, b) (((a)%mod * (b)%mod)%mod)
#define init(arr, val) memset(arr, val, sizeof(arr))

const ll mod = 1e9 + 7;

using namespace std;

void setIO(const string& file_name){
    freopen((file_name+".in").c_str(), "r", stdin);
    freopen((file_name+".out").c_str(), "w+", stdout);
}
int m[max_v], low[max_v], vis[max_v];
ll freq[max_v], p[max_v], n, k, ans[max_v], contr[max_v];
//this'll hurt my brain for sure
//mew(1) is 1
//mew(2) is -1
//mew(3) is -1
//mew(4) is 0
//mew(5) is -1
//mew(6) is 1
//hopefully this'll work for my brick of a brain

ll bin_pow(ll a, ll b){
  ll ans = 1ll;
  for(int i = 0; pow_2(i) <= b; i++){
    if(b&pow_2(i)){
      ans = mul(ans, a);
    }
    a = mul(a, a);
  }
  return ans;
}

int main(){
    cin.tie(0) -> sync_with_stdio(0);
  low[1] = mod; //1 -> 0 for a better progression
  m[1] = 1;
  //seive for primes, low[i] is the smallest prime that divides i
  for(int i = 2; i<=2e6; i++){
    if(vis[i]) cont;
    for(int j = i; j<=2e6; j += i){
      if(!vis[j]) low[j] = i;
      vis[j] = 1;
    }
  }
  //compute m, or mobius's function
  for(int i = 2; i <=2e6; i++){
    if(low[i] == i) m[i] = -1;
    else if((i/low[i])%low[i] == 0) m[i] = 0;
    else m[i] = m[i/low[i]] * -1;
  }

  cin >> n >> k;
  //compute each i^n
  for(int i = 1; i<=k; i++){
    p[i] = bin_pow(i, n);
  }
  ll tot = 0ll;

  for(int i = 1; i<=k; i++){
    ans[i] = ans[i - 1]; //the current answer is similar to the prior one
    for(int j = i; j; j /= low[j]){
      ans[i] = add(ans[i], mod - contr[j]); //the only differences are the numbers
      contr[j] = mul(mod + m[j], p[i/j]);   //that evenly divide i
      ans[i] = add(ans[i], contr[j]);       //thats what this is for
    }

    //cout << ans[i] << ' ' << (int)(ans[i]^(ll)i) << endl;
    tot = add(tot, ans[i] ^ (ll)i);
  }

  cout << tot << '\n'; //WHY IS IT WA. WHY WHY WHY
  return 0;
}