md = 10**9+7

from array import array

n = int(input())
cnt = array("I", [0]*n)
for _ in range(n):
    a = int(input())
    cnt[a] += 1

dp = array("L", [1]+[0]*n)
for a in range(n):
    if cnt[a] == 0: continue
    for i in range(n)[::-1]:
        dp[i+1] += dp[i]*cnt[a]%md

ans = 0
f = 1
for i in range(n+1)[::-1]:
    cur = dp[i]*f%md
    if i & 1:
        ans -= cur
    else:
        ans += cur
    ans %= md
    f = f*(n+1-i)%md

print(ans)