#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N=5010,mod=1e9+7;
int n,x,ans,cnt[N],g[2][N],f[N],pre[N];
signed main(){
	ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
	cin>>n,pre[0]=g[0][0]=1;
	for(int i=1;i<=n;i++)cin>>x,cnt[x+1]++,pre[i]=pre[i-1]*i%mod; 
	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]*cnt[i])%mod;
	}
	for(int i=0;i<=n;i++)f[i]=g[n&1][i]*pre[n-i]%mod;
	for(int i=0;i<=n;i++)ans=(ans+((i&1)?mod-f[i]:f[i]))%mod;
	cout<<ans<<"\n";
	return 0;
}