import java.util.Scanner;

public class Main {
	private final int MOD = 1000000007;

	public void solve() {
		Scanner scanner = new Scanner(System.in);
		int N = scanner.nextInt();
		int[] hates = new int[N];
		for (int i = 0; i < N; i++) {
			hates[scanner.nextInt()]++;
		}
		scanner.close();

		// dp[i][j]:= i番目の出席番号までだけ見て、
		// j個の出席番号が嫌いな人に割り当てられている数
		long[][] dp = new long[N + 1][N + 1];
		dp[0][0] = 1;
		for (int i = 0; i < N; i++) {
			for (int j = N; j >= 0; j--) {
				dp[i + 1][j] = dp[i][j];
				if (j == 0) {
					continue;
				}
				dp[i + 1][j] += dp[i][j - 1] * hates[i];
				dp[i + 1][j] %= MOD;
			}
		}

		// factor[i] = i!
		long[] factor = new long[N + 1];
		factor[0] = 1;
		for (int i = 1; i <= N; i++) {
			factor[i] = factor[i - 1] * i;
			factor[i] %= MOD;
		}

		long ans = 0;
		for (int j = 0; j <= N; j++) {
			if (j % 2 == 0) {
				ans += dp[N][j] * factor[N - j] % MOD;
			} else {
				ans -= dp[N][j] * factor[N - j] % MOD;
			}
		}
		System.out.println(ans);
	}

	public static void main(String[] args) {
		new Main().solve();
	}
}