C++ :

#include<cstdio>
#define N 1000000
#define LL long long
#define mo 1000000007
using namespace std;
int n,k;
int f[N+5],inv[N+5],fac[N+5];
main()
{
    scanf("%d%d",&n,&k);
    fac[0]=1;inv[0]=inv[1]=1;
    for (int i=1;i<=n;++i) fac[i]=fac[i-1]*(LL)i%mo;
    for (int i=2;i<=n;++i) inv[i]=(LL)(mo-mo/i)*inv[mo%i]%mo;
    for (int i=2;i<=n;++i) inv[i]=inv[i]*(LL)inv[i-1]%mo;
    int sum=0,ans=0,t=2;
    for (int i=n;i>=k;--i)
    {
        sum=(LL)fac[n]*inv[k]%mo*inv[n-i]%mo*inv[i-k]%mo*(t-1)%mo;
        t=(LL)t*t%mo;
        if (i-k&1) ans-=sum;
        else ans+=sum;
        if (ans>=mo) ans-=mo;
        if (ans<=-mo) ans+=mo;
    }
    printf("%d\n",(ans+mo)%mo);
}