import sys
input = lambda : sys.stdin.readline().rstrip()

sys.setrecursionlimit(2*10**5+10)
write = lambda x: sys.stdout.write(x+"\n")
debug = lambda x: sys.stderr.write(x+"\n")
writef = lambda x: print("{:.12f}".format(x))

import numpy as np
n = int(input())
a = ([int(input()) for _ in range(n)])
count = [0]*n
for v in (a):
    count[v] += 1
M = 10**9+7
ans = 0
dp = np.zeros(n+1, dtype=np.int64)
dp[0] = 1
for k in range(n):
    v = count[k]
    if v==0:
        continue
    ndp = np.array(dp)
    ndp[1:] += dp[:-1]*v%M
    dp = ndp
#     for b in range(n):
#         val = dp[b]
#         if val==0:
#             continue
#         ndp[b] += val
#         ndp[b+1] += v*val%M
#         ndp[b] %= M
#         ndp[b+1] %= M
#     dp = ndp
g = [1]
dp = dp.tolist()
for i in range(1,n+1):
    g.append(g[-1]*i%M)
s = 1
for i in range(n+1):
    ans += s * dp[i] * g[n-i] % M
    ans %= M
    s *= -1
print(ans%M)