#include<bits/stdc++.h>
#define int long long
using namespace std;
const int mod=1e9+7;
int n,x,a[5005],f[5005],g[2][5005],jie[5005],ans=0;
signed main(){
    ios::sync_with_stdio(0);
    cin.tie(0),cout.tie(0);
    cin>>n;jie[0]=1;
    for(int i=1;i<=n;i++)cin>>x,a[x+1]++,jie[i]=jie[i-1]*i%mod;
    g[0][0]=1;
    for(int i=1;i<=n;i++){
        memset(g[i&1],0,sizeof(g[i&1]));
        g[i&1][0]=1;
        for(int j=1;j<=i;j++)g[i&1][j]=(g[(i&1)^1][j]+g[(i&1)^1][j-1]*a[i])%mod;
    }
    for(int i=0;i<=n;i++)f[i]=jie[n-i]*g[n&1][i]%mod;
    for(int i=0;i<=n;i++)ans=(ans+((i&1)?mod-f[i]:f[i]))%mod;
    cout<<ans;
    return 0;
}