#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define MP make_pair
mt19937 rnd(time(0));
const int MOD=1e9+9;
const int MAXN=5e5+5;
ll ksm(ll a,int b){ll r=1;while(b){if(b&1)r=r*a%MOD;a=a*a%MOD,b>>=1;}return r;}
ll n,a[MAXN];
ll fac[MAXN],inf[MAXN];
void solve(){
	cin>>n;
	for(int i=1;i<=n;i++) cin>>a[i];
	sort(a+1,a+n+1);
	ll s=a[1]+a[n];
	for(int i=1;i<=n;i++) if(s!=a[i]+a[n+1-i]){
		cout<<0<<endl;
		return;
	}
	ll ans=fac[n/2];
	map<int,int> mp;
	for(int i=1;i<=n/2;i++){
		mp[a[i]]++;
		if(a[i]!=a[n+1/2]) ans=ans*2%MOD;
	}
	for(auto i:mp) ans=ans*inf[i.second]%MOD;
	cout<<ans<<endl;
}
int main(){
	ios::sync_with_stdio(false);
	fac[0]=inf[0]=1;
	for(int i=1;i<MAXN;i++) inf[i]=ksm(fac[i]=fac[i-1]*i%MOD,MOD-2);
	int _;cin>>_;
	while(_--) solve();
	return 0;
}