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| #include<bits/stdc++.h>
#define RG register
#define file(x) freopen(#x".in", "r", stdin);freopen(#x".out", "w", stdout);
#define clear(x, y) memset(x, y, sizeof(x));
using namespace std;
inline int read()
{
int data=0, w=1;
char ch=getchar();
while(ch!='-'&&(ch<'0'||ch>'9')) ch=getchar();
if(ch=='-') w=-1, ch=getchar();
while(ch>='0'&&ch<='9') data=(data<<3)+(data<<1)+(ch^48), ch=getchar();
return data*w;
}
const int maxn(510), yl(1e9+7);
int f[maxn][maxn * maxn], frac[maxn], inv[maxn], n, e, T, c[maxn][maxn];
inline int fastpow(int x, int y)
{
int base=x%yl, ans=1;
while(y)
{
if(y&1) ans=(1ll*ans*base)%yl;
base=(1ll*base*base)%yl;
y>>=1;
}
return ans%yl;
}
int main()
{
frac[0]=1;
for(RG int i=1;i<=maxn-5;i++) frac[i]=1ll*frac[i-1]*i%yl, inv[i]=fastpow(frac[i], yl-2);
f[1][0]=f[1][1]=1;
for(n=2;n<=maxn-5;n++)
{
for(e=0;e<=(n-1)*n>>1;e++)
{
f[n][e]=f[n-1][e];
if(e-n>=0) f[n][e]=(1ll*f[n][e]-1ll*f[n-1][e-n]+yl)%yl;
if(e>0) f[n][e]=(1ll*f[n][e]+1ll*f[n][e-1])%yl;
}
for(e=((n-1)*n>>1)+1;e<=(n+1)*n>>1;e++) f[n][e]=f[n][e-1];
}
T=read();
#define sqr(a) ((1ll*(a))*(1ll*(a))%yl)
while(T--)
{
n=read(); e=read(); long long ans=0;
for(RG int i=1;i<=n;i++)
ans=(1ll*ans+1ll*f[i][min(e, (i-1)*i>>1)]*(n-i+1)%yl*sqr(1ll*frac[n]*inv[i]%yl)%yl)%yl;
printf("%lld\n", ans);
}
return 0;
}
|