#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int maxn = 605;
const int mod = int(1e9) + 7;
ll binpow(ll a,ll b)
{
return (b == 0 ? 1 : (b%2 == 0 ? binpow((a*a)%mod,b/2) : (a*binpow(a,b-1))%mod));
}
ll del(ll a,ll b)
{
return (a*binpow(b,mod-2))%mod;
}
ll cnk[2*maxn][2*maxn];
int dp[maxn][maxn];
int dp2[maxn][2*maxn];
int fact[2*maxn];
int a[maxn];
int ans =0;
vector<int> tk;
void rec(int pos,int n)
{
if(pos == 2*n)
{
vector<int> vis(n+1);
vis[0] = 1;
vector<int> s;
for(int j = 2*n-1;j >= 0;--j)
{
// cout << tk[j];
for(int u = tk[j];u >= 0;u--)
{
if(!vis[u])
{
s.push_back(j+1);
vis[u] = 1;
break;
}
}
}
int no = 0;
for(int u = n-1;u >= 0;--u)
{
if(a[u] != s[n-u-1])
{
no = 1;
}
}
ans += (!no);
return ;
}
for(int j = 1;j <= n;++j)
{
int v = 0;
for(int u = 0;u < tk.size();++u)
{
if(tk[u] == j)
v++;
}
if(v < 2)
{
tk.push_back(j);
rec(pos+1,n);
tk.pop_back();
}
}
}
int solve_stupid(int n)
{
tk.clear();
ans = 0;
rec(0,n);
return ans;
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
for(int i = 0;i < 2*maxn;++i)
{
for(int j = 0;j <= i;++j)
{
cnk[i][j] = (j == 0 ? 1 : (j == i ? 1 : (cnk[i-1][j] + cnk[i-1][j-1])%mod));
}
}
fact[0] = 1;
for(int i = 1;i < 2*maxn;++i)
{
fact[i] = (fact[i-1]*i)%mod;
}
int n;
cin >> n;
for(int i = 0;i < n;++i)
{
cin >> a[i];
}
for(int i = 0;i <= n;++i)
{
for(int j = 0;j <= 2*n;++j)
{
if(i == 0)
{
dp2[i][j] = 1;
}
else
{
if(j == 0 || j <= 2*(i-1))
dp2[i][j] = 0;
else
dp2[i][j] = (dp2[i][j-1] + dp2[i-1][j-1])%mod;
}
}
}
// cout << dp2[2][4] << ' ';
if(a[n-1] != 2*n)
{
cout << 0;
return 0;
}
dp[0][n] = 1;
for(int i = 1;i <= n;++i)
{
for(int m = 0;m <= n;++m)
{
dp[i][m] = 0;
for(int mn = m;mn <= n;++mn)
{
if(mn == m)
{
int r = 2*n-a[i-1];
int re = n-i;
int cmn = r-re + mn;
int rem = 2*mn-cmn;
int pl = (a[i-1] - (i == 1 ? 0 : a[i-2]) - 1);
if(r >= re && rem >= pl)
{
dp[i][m] = (dp[i][m] + (dp[i-1][mn] * cnk[rem][pl])%mod * fact[pl])%mod;
}
}
else
{
int r = 2*n-a[i-1];
int re = n-i;
int cmn = r-re + mn;
int rem = 2*mn-cmn;
int pl = (a[i-1] - (i == 1 ? 0 : a[i-2]) - 1);
if(r >= re && rem >= pl && re+1 >= mn)
{
ll w = ((((dp2[mn-m-1][2*(mn-m-1)] * cnk[re-m][mn-m-1])%mod) * (mn-m+1))%mod * fact[mn-m-1])%mod;
dp[i][m] = (dp[i][m] + ((dp[i-1][mn] * cnk[rem][pl])%mod * w)%mod * fact[pl])%mod;
}
}
}
//cout << dp[i][m] << ' ';
}
// cout << "\n";
}
cout << del(dp[n][0],binpow(2,n));
return 0;
}
