#include <bits/stdc++.h>
using namespace std;
#define cerr cerr << "DEBUG "
constexpr int MOD = 1000 * 1000 * 1000 + 7;
void add(int &a, int b) {
a += b;
if (a >= MOD) {
a -= MOD;
}
}
int mult(int a, int b) {
return 1ll * a * b % MOD;
}
int inv(int n) {
int k = MOD - 2;
int res = 1;
for (; k; k >>= 1, n = mult(n, n)) {
if (k & 1) {
res = mult(res, n);
}
}
return res;
}
constexpr int N = 3e3 + 10;
int n, dp[N], p[N];
int ncr[N][N];
bool used[N];
int main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
ncr[0][0] = 1;
for (int i = 0; i < N; ++i) {
for (int j = 0; j < N; ++j) {
if (i + j) {
ncr[i][j] = (i ? ncr[i - 1][j] : 0);
add(ncr[i][j], (i && j ? ncr[i - 1][j - 1] : 0));
}
}
}
p[0] = 1;
for (int i = 1; i < N; ++i) {
for (int j = 0; j < i; ++j) {
add(p[i], mult(ncr[i - 1][j], mult(i - j + 1, mult(p[j], p[i - j - 1]))));
}
}
cin >> n;
for (int i = 0; i < n; ++i) {
int x;
cin >> x;
used[x] = true;
}
dp[0] = 1;
int cnt[2] = {};
for (int k = n << 1; k > 0; --k) {
if (used[k]) {
for (int i = cnt[1] + 1; i >= 0; --i) {
for (int j = 0; j < i; ++j) {
add(dp[i], mult(mult(dp[j], mult(i - j + 1, p[i - j - 1])), ncr[cnt[1] - j][i - j - 1]));
}
}
} else {
for (int i = 0; i <= cnt[1]; ++i) {
dp[i] = mult(dp[i], max(0, i - cnt[0]));
}
}
cnt[used[k]]++;
//cerr << used[k] << '\n';
/*for (int i = 0; i <= cnt[1]; ++i) {
cerr << "dp[" << i "] = " << dp[i] << '\n';
}*/
}
int pw = 1;
for (int i = 0; i < n; ++i) {
pw = mult(pw, 2);
}
cout << mult(dp[n], inv(pw));
}
