#include<bits/stdc++.h>
#define ll long long
using namespace std;
ll n,a[200005],tp,nm,b[200005],m,md=1000000007,tm2[200005],jc[200005],ans;
ll tme2(ll m){
	if(tm2[m]>0)
		return tm2[m];
	return tm2[m]=tme2(m/2)*tme2(m/2)%md*(m%2?2:1)%md;
}//check
ll t(ll n,ll m){
 	if(m==0)
		return 1;
	ll res=t(n,m/2);
	return res*res%md*(m%2?n:1)%md;
}//check
ll C(ll n,ll m){
	m=min(m,n-m);
	return jc[n]*t(jc[n-m],md-2)%md*t(jc[m],md-2)%md;
}
int main(){
	jc[0]=tm2[0]=1;
	scanf("%lld",&n);
	for(int i=1;i<=n;++i){
		jc[i]=jc[i-1]*i%md;
		scanf("%lld",a+i);
		++b[a[i]];
	}
	for(int i=1;i<=n;++i)
		for(;b[i];--b[i])
			a[++m]=i;//check
	for(int i=1;i<=n;++i)
		if(a[i]<=i)
			ans=(ans+C(i-1,a[i]-1)*tme2(n-i)%md)%md;
	printf("%lld",ans);
}