#include<bits/stdc++.h>
typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
#define pii pair<ll,ll>
#define rep(i,a,b) for(ll i=(a);i<=(b);++i)
#define per(i,a,b) for(ll i=(a);i>=(b);--i)
using namespace std;
bool Mbe;
ll read(){
    ll x=0,f=1;char ch=getchar();
    while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
    return x*f;
}
void write(ll x){
    if(x<0)putchar('-'),x=-x;
    if(x>9)write(x/10);
    putchar(x%10+'0');
}
const ll N=155,Mod=1e9+7;
ll n,m,dp[N][N*N][2];
ll pw(ll x,ll p){
    ll res=1;
    while(p){
        if(p&1)res=res*x%Mod;
        x=x*x%Mod,p>>=1;
    }
    return res;
}
void Upd(ll&x,ll y){
    x+=y;
    if(x>=Mod)x-=Mod;
}
bool Med;
int main(){
    cerr<<fabs(&Med-&Mbe)/1048576.0<<"MB\n";
    n=read(),m=read();
    if(n==2)return puts("0"),0;
    dp[0][0][0]=1;
    rep(i,1,n+1){
        if(i==m)continue;
        rep(j,0,i-1){
            rep(k,0,i*(i+1)/2){
                rep(l,0,1)Upd(dp[i][k+(i-j-1)*(i-j)/2][l],Mod-dp[j][k][l]);
                Upd(dp[i][k+(i-j-1)*(i-j)/2][1],Mod-dp[j][k][0]*(i-j-1-(j<m&&m<i))%Mod);
            }
        }
    }
    ll iv=pw(n*(n+1)/2,Mod-2),ans=0;
    rep(i,0,n*(n+1)/2)ans=(ans+dp[n+1][i][1]*pw(1-iv*i%Mod+Mod,Mod-2))%Mod;
    write(ans*pw(n-1,Mod-2)%Mod);
    cerr<<"\n"<<clock()*1.0/CLOCKS_PER_SEC*1000<<"ms\n";
    return 0;
}