import std.conv, std.functional, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.complex, std.container, std.math, std.numeric, std.range, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }
real readReal() { return readToken.to!real; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }


enum MO = 10L^^9 + 7;
enum LIM = 10^^5;

long[] inv, fac, invFac;
void prepare() {
  inv = new long[LIM];
  fac = new long[LIM];
  invFac = new long[LIM];
  inv[1] = 1;
  foreach (i; 2 .. LIM) {
    inv[i] = MO - ((MO / i) * inv[cast(size_t)(MO % i)]) % MO;
  }
  fac[0] = invFac[0] = 1;
  foreach (i; 1 .. LIM) {
    fac[i] = (fac[i - 1] * i) % MO;
    invFac[i] = (invFac[i - 1] * inv[i]) % MO;
  }
}
long binom(long n, long k) {
  if (0 <= k && k <= n) {
    assert(n < LIM);
    return fac[cast(size_t)(n)] * invFac[cast(size_t)(k)] % MO * invFac[cast(size_t)(n - k)] % MO;
  } else {
    return 0;
  }
}


int N;
int[] A;

void main() {
  prepare();
  
  try {
    for (; ; ) {
      N = readInt();
      A = new int[N];
      foreach (i; 0 .. N) {
        A[i] = readInt();
      }
      
      auto cnt = new int[N];
      foreach (i; 0 .. N) {
        if (0 <= A[i] && A[i] < N) {
          ++cnt[A[i]];
        }
      }
      auto dp = new long[N + 1];
      dp[0] = 1;
      foreach (j; 0 .. N) {
        auto dpNext = new long[N + 1];
        foreach (x; 0 .. N + 1) {
          (dpNext[x] += dp[x]) %= MO;
          if (x + 1 <= N) {
            (dpNext[x + 1] += dp[x] * cnt[j]) %= MO;
          }
        }
        dp = dpNext;
      }
      long ans;
      foreach (x; 0 .. N + 1) {
        ans += ((x % 2 != 0) ? -1 : +1) * dp[x] * fac[N - x];
        ans %= MO;
      }
      ans = (ans % MO + MO) % MO;
      writeln(ans);
    }
  } catch (EOFException e) {
  }
}