Problem:
Score : 500 points

Problem Statement

Consider sequences \{A_1,...,A_N\} of length N consisting of integers between 1 and K (inclusive).

There are K^N such sequences. Find the sum of \gcd(A_1, ..., A_N) over all of them.

Since this sum can be enormous, print the value modulo (10^9+7).

Here \gcd(A_1, ..., A_N) denotes the greatest common divisor of A_1, ..., A_N.

Constraints

2 \leq N \leq 10^5

1 \leq K \leq 10^5

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N K

Output

Print the sum of \gcd(A_1, ..., A_N) over all K^N sequences, modulo (10^9+7).

Sample Input 1

3 2

Sample Output 1

9

\gcd(1,1,1)+\gcd(1,1,2)+\gcd(1,2,1)+\gcd(1,2,2)
+\gcd(2,1,1)+\gcd(2,1,2)+\gcd(2,2,1)+\gcd(2,2,2)
=1+1+1+1+1+1+1+2=9

Thus, the answer is 9.

Sample Input 2

3 200

Sample Output 2

10813692

Sample Input 3

100000 100000

Sample Output 3

742202979

Be sure to print the sum modulo (10^9+7).

Solution in C (GCC 9.2.1) (judge verdict: Accepted)

#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include<string.h>
#include<stdbool.h>
typedef long long ll;
typedef long double ld;
#define rep(i,l,r)for(ll i=(l);i<(r);i++)
#define repp(i,l,r,k)for(ll i=(l);i<(r);i+=(k))
#define rrep(i,l,r)for(ll i=(l);i>=(r);i--)
#define INF (1LL<<60)
#define MOD1 1000000007
#define MOD2 998244353
#define MAX_N (1 << 17)
#define YES printf("Yes\n")
#define NO printf("No\n")
#define PN printf("\n")

void swap(ll *a, ll *b){ll c;c=*b;*b=*a;*a=c;}
ll max2(ll a,ll b){return a>=b?a:b;}
ll min2(ll a,ll b){return a>=b?b:a;}
ll min3(ll a, ll b, ll c){return (a<=b && a<=c) ? a : b<=c ? b : c;}
ll max3(ll a, ll b, ll c){return (a>=b && a>=c) ? a : b>=c ? b : c;}
ll minn(ll n, ll a[n]){ll b=INF;rep(i,0,n) b=min2(b,a[i]);return b;}
ll maxn(ll n, ll a[n]){ll b=-INF;rep(i,0,n) b=max2(b,a[i]);return b;}
ll ABS(ll a){return a>=0?a:(-a);}
ll POW(ll a, ll b){ll c=1;rep(i,0,b) c*=a;return c;}
ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
ll lcm(ll a,ll b){return a/gcd(a,b)*b;}
ll mod(ll n){return n%=MOD1;}
int upll(const void*a, const void*b){return*(ll*)a<*(ll*)b?-1:*(ll*)a>*(ll*)b?1:0;}
int downll(const void*a, const void*b){return*(ll*)a<*(ll*)b?1:*(ll*)a>*(ll*)b?-1:0;}
void sortup(ll*a,int n){qsort(a,n,sizeof(ll),upll);}
void sortdown(ll*a,int n){qsort(a,n,sizeof(ll),downll);}

typedef struct{ ll a , b;}fr;
int cmp1( const void *p, const void *q ) { return ((fr*)p) ->a - ((fr*)q)->a;}
int cmp2( const void *p, const void *q ) { return ((fr*)q) ->a - ((fr*)p)->a;}
void strsortup(fr*a,int n){qsort(a,n,sizeof(fr),cmp1);}
void strsortdown(fr*a,int n){qsort(a,n,sizeof(fr),cmp2);}

/*aのb進数時の桁数*/
ll digits(ll a, ll b){return a/b?1+digits(a/b,b):1;}
/*nをa進数にしたときの、i桁目の数*/
ll placenai(ll n, ll a, ll i){return i==1?n%a:placenai(n/a,a,i-1);}
/*aのn乗(mod) 繰り返し二乗法*/
ll modpow(ll a, ll n, ll mod){
    ll s[digits(n,2)],ans=1;
    rep(i,0,digits(n,2)){
        s[i]= i==0 ? a : s[i-1]*s[i-1]%mod ;
        ans*=placenai(n,2,i+1)==1?s[i]:1; ans%=mod;
    }
    return n?ans:1;
}
ll inv[200005],finv[200005];
void makeinv(ll n){
    inv[1]=1;finv[0]=finv[1]=1;
    rep(i,2,n+1){
        inv[i]=MOD1 - inv[MOD1%i] * (MOD1 / i) % MOD1;
        finv[i] = finv[i - 1] * inv[i] % MOD1;
    }
}
ll modfac(ll n, ll mod){
    ll x=1;
    rep(i,2,n+1){x*=i%mod;x%=mod;}
    return x;
}

int main(void){
    // char ;
    ll n,k,ans=0;
    scanf("%lld%lld",&n,&k);
    ll pat[k];
    rrep(i,k,1){
        ll plus=modpow(k/i,n,MOD1);
        rep(j,2,k+1){
            if(i*j>k) break;
            plus-=pat[i*j-1];
        }
        if(plus<0){
            plus+=ABS(plus)/MOD1*MOD1;
        }
        while(plus<0) plus+=MOD1;
        pat[i-1]=plus;
        ans+=i*plus;
        ans%=MOD1;
        // printf("%lld ",ans);
    }
    
    printf("%lld\n",ans);
    return 0;
}