#include
     
      #define ll long longint p=1e9+7;ll fastpow(ll x,ll k){    ll b=1;    while (k>0)    {          if (k%2==1)             b=(b*x)%p;          k=k/2;          x=(x*x)%p;    }    b=b%p;    return b;} int n,m;int main(){     scanf("%d%d",&n,&m);ll sum=m;                   for(int i=2;i<=n;i++)    {        ll w=fastpow(i,m);                sum+=((i*((w-1+p)%p))%p*fastpow(i-1,p-2))%p;                sum%=p;	    }    printf("%d",int(sum));        }
     

ax ≡ 1 (mod b)

b^-1x≡1

a,b互质

x^b-1≡ 1(mod b)

a*x^-1(mod b)=a*x^b-2(mod b)