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))


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 = [0]*(n+1)
dp[0] = 1
for k in range(n):
    v = count[k]
    if v==0:
        continue
    ndp = [0]*(n+1)
    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]
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)