#include <bits/stdc++.h>
using namespace std;
const int maxn = 605;
const long long mod = 1e9 + 7;
long long ways[maxn];
int a[maxn];
int var;
long long mem[maxn][maxn];
long long C[maxn * 2][maxn * 2];
long long fac[] = {1, 1, (mod + 1) / 2};
long long calc(int cur, int take) {
long long ans = 0;
if(cur == 1) {
for(int i = 0; i <= 2; i++) {
if(take + i == var + 1) {
return (C[take + i][i] * (fac[2 - i])) % mod;
}
}
return 0;
}
if(mem[cur][take] != -1) return mem[cur][take];
for(int i = 0; i <= 2; i++) {
if(take + i <= var - cur + 1) {
long long add = (calc(cur - 1, take + i) * C[take + i][i]) % mod;
ans += (add * (fac[2 - i])) % mod;
ans %= mod;
}
}
return mem[cur][take] = ans;
}
long long dp[maxn][maxn];
int main() {
int n;
cin >> n;
for(int i = 1; i <= n; i++) cin >> a[i];
for(int i = 0; i <= n + n; i++) {
C[i][0] = 1;
for(int j = 1; j <= i; j++) {
C[i][j] = (C[i - 1][j] + C[i - 1][j - 1]) % mod;
}
}
for(int i = 1; i <= n; i++) {
memset(mem, -1, sizeof mem);
var = i;
ways[i] = calc(var, 0);
}
memset(mem, -1, sizeof mem);
dp[n][0] = 1;
for(int cur = n - 1; cur >= 0; cur--) {
for(int bound = 0; bound <= n; bound++) {
dp[cur][bound] = (1LL * dp[cur + 1][bound] * (n - bound - cur)) % mod;
for(int i = 0; i < bound; i++) {
int free = a[cur + 1] - (n - bound + (cur + 1));
if(free >= bound - i) {
long long add = ((C[free][bound - i] * ways[bound - i] % mod) * dp[cur + 1][i]) % mod;
dp[cur][bound] += add;
dp[cur][bound] %= mod;
}
}
}
}
cout << dp[0][n] << endl;
return 0;
}
