/*-----------------------------------------------*/
/* Everything that kills me makes me feel alive. */
/* Email: [email protected]                  */
/* Author: wzj_zhzx_oicon / BreakPlus            */
/*-----------------------------------------------*/
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll,ll> P;
typedef pair<pair<ll,ll>,ll> P3;
typedef pair<pair<ll,ll>,pair<ll,ll> >P4;
#define mkp make_pair
#define fi first
#define se second
#define popcnt __builtin_popcountll
#define pb emplace_back
//#define FastIO
//#define OIcontest
const ll mod=1e9+7;
const ll maxn=500005;

inline 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;
}
inline ll lowbit(ll x){ return x&-x; }
struct Bit{
	ll c[maxn], _x[maxn], _w[maxn], tp=0;
	void update(ll x,ll w){ _x[++tp]=x, _w[tp]=w; while(x<maxn) c[x]+=w, x+=lowbit(x);}
	void update2(ll x,ll w){ while(x<maxn) c[x]+=w, x+=lowbit(x);}
	ll query(ll x){ ll res=0; while(x) res+=c[x], x-=lowbit(x); return res; }
	void clear(){ for(ll i=1;i<=tp;i++) update2(_x[i], -_w[i]); tp=0;}
	void fclear(){ tp=0; memset(c, 0, sizeof(c)); }
}bit;

inline ll maxx(ll a,ll b){ return a>b?a:b; }
inline ll minn(ll a,ll b){ return a<b?a:b; }
inline void chkmax(ll &a,ll b){ a = maxx(a, b); }
inline void chkmin(ll &a,ll b){ a = minn(a, b); }

inline void _Add(ll &a,ll b){ a+=b; if(a>=mod) a-=mod; }
inline void _Minus(ll &a,ll b){ a-=b; if(a<0) a+=mod; }
inline ll Add(ll a,ll b){ a+=b; if(a>=mod) a-=mod; return a; }
inline ll Minus(ll a,ll b){ a-=b; if(a<0) a+=mod; return a; }

inline ll qpow(ll a,ll b){
    ll ans=1, base=a;
    while(b){ if(b&1) ans=1ll*ans*base%mod; base=1ll*base*base%mod; b>>=1; }
    return ans;
}
struct Comb{
    ll fac[maxn], inv[maxn];
    Comb(){
       fac[0]=1; for(ll i=1;i<=maxn-5;i++) fac[i]=1ll*fac[i-1]*i%mod;
	   inv[maxn-5]=qpow(fac[maxn-5],mod-2); for(ll i=maxn-6;i>=0;i--) inv[i]=1ll*inv[i+1]*(i+1)%mod;
    }
    ll C(ll a,ll b){ if(a<0 || b<0 || a<b) return 0; return 1ll*fac[a]*inv[b]%mod*inv[a-b]%mod; }
}comb;
ll Fac(ll x){return comb.fac[x];}ll iFac(ll x){return comb.inv[x];}ll Inv(ll x){return qpow(x, mod-2);}
/*--------------head------------------*/
void init(){

}
void clear(){  }
ll n,m,dp[155][13005][2], w1[160], w2[160], t;
void solve(){
	n=read(), m=read();
	dp[0][0][0] = 1;
	for(ll i=0;i<n;i++)
		for(ll j=0;j<n*(n+1)/2;j++)
		for(ll k=0;k<=1;k++){
			if(!dp[i][j][k]) continue;
			for(ll l=i+1;l<=n;l++){
				ll mor = (i<m && l>=m) ? ((l-i) * (l-i+1)/2) : ((l-i) * (l-i-1) / 2);
				if(!k) _Add(dp[l][j+mor][1], mod-dp[i][j][k]);
				_Add(dp[l][j+mor][k], mod-dp[i][j][k]);
			}
		}
	ll ans=0, is = qpow(n-1, mod-2);
	for(ll j=0;j<n*(n+1)/2;j++){
		ll tmp = n*(n+1)/2*Inv(n*(n+1)/2-j)%mod;
		_Add(ans, tmp * dp[n][j][0] % mod * n % mod * is % mod);
		_Add(ans, mod - tmp * dp[n][j][1] % mod * is % mod);
	}
	printf("%lld\n", ans);
}
int main(){
    #ifdef OIcontest
        freopen(".in","r",stdin);
        freopen(".out","w",stdout);
    #endif
    #ifdef FastIO
        ios::sync_with_stdio(0); cin.tie(0), cout.tie(0);
    #endif
    init();
    ll T=1;
    while(T--) clear(), solve();
    return 0;
}
/*
Input1 Text Copied:


Answer1 Text Copied:


Input2 Text Copied:


Answer2 Text Copied:
*/