#include <bits/stdc++.h>
#define il inline
using namespace std;
typedef long long ll;
const ll mod=1e9+7;
il ll qp(ll a,ll b){
    ll ans=1ll;
    while(b){
        if(b&1) ans=(ans*a)%mod;
        a=(a*a)%mod,b>>=1;
    }return ans;
}
il void add(ll &x,ll y){x=(x+y>=mod?x+y-mod:x+y);}
il void del(ll &x,ll y){x=(x<y?x-y+mod:x-y);}
il int pc(int x){
    int s=0;
    while(x) ++s,x-=(x&-x);
    return s;
}
const int N=20;
ll f[1<<N],a[1<<N],inv[(N+2)*(N+2)];int b[N],to[N],c[N][N];
il int get(int l,int r){return l?((1<<(r+1))-(1<<l)):(1<<(r+1))-1;}
il ll solve(int n,int u,int v){//u:wolf,v:predictor
    if(n==2) return 0ll;
    int S=(1<<(n-1)),x=0,y,z,mul=(n*(n+1ll))/2ll;ll w,ret=0ll;
    for(int i=0;i<n;++i){
        if(i==v) continue;
        b[x]=i,to[i]=x,++x;
    }
    for(int i=0;i<n;++i){
        c[i][i]=(1<<to[i])*(i!=v);
        for(int j=i+1;j<n;++j){
            c[i][j]=c[i][j-1]+(1<<to[j])*(j!=v);
        }
    }
    for(int i=0;i<S;++i) f[i]=0ll;
    f[1<<to[u]]=0ll;
    for(int i=(1<<to[u])+1;i<S;++i){
        if(!((i>>to[u])&1)) continue;
        y=0,w=0ll;
        for(int l=0;l<n;++l)
            for(int r=l;r<n;++r){
                x=c[l][r];if(u<l || u>r) x=S-1-x;
                x&=i;if(x==i) ++y;else add(w,f[x]);
            }
        //w=(w+(mul-y)*inv[mul])%mod;printf("%d %d %lld\n",i,y,w);
        f[i]=((w+mul)*inv[mul-y])%mod;
    }
    return f[S-1];
}
int n,m;ll ans;
il void init(){
    inv[0]=1ll;
    for(int i=1;i<=n*n;++i) inv[i]=qp(i,mod-2ll);
}
int main(){
    scanf("%d%d",&n,&m);init();
    for(int i=1;i<=n;++i) if(i!=m) ans=(ans+solve(n,m-1,i-1))%mod;
    printf("%lld",(ans*qp(n-1ll,mod-2ll))%mod);
    return 0;
}