M=10**9+7
c=[0]*5000
N=input()
for i in xrange(N):c[input()]+=1
a=[1]+[0]*N
p=[1]+[0]*N
for i in xrange(N):
	p[i+1]=p[i]*(i+1)%M
	for j in xrange(N,0,-1):a[j]=(a[j]+a[j-1]*c[i])%M
r=0
for i in xrange(N+1):r=(r+(-1)**(i%2)*a[i]*p[N-i])%M
print r