from sys import stdin
from collections import defaultdict
M=10**9+7
c=defaultdict(int)
N=int(stdin.readline())
for i in range(N):c[int(stdin.readline())]+=1
a=[1]+[0]*N
f=list(a)
for i in range(N):
	f[i+1]=f[i]*-~i%M
	for j in range(N,0,-1):a[j]=(a[j]+a[j-1]*c[i])%M
r=0
for i in range(N+1):r=(r+(-1)**(i%2)*a[i]*f[N-i])%M
print(r)