N = int(input())
x = list(map(int,input().split()))

P = 10 ** 9 + 7
t = 0
X = sum(x)
r = pow(X,P-2,P)
rr = pow(X - 1,P-2,P)
rrr = pow(2,P-2,P)
for a in x:
    t += a * (a - 1) % P * rr % P * r % P
    t %= P
t = (1 - t) % P
print((t * (sum(x)-1) + 1) % P)