class Integer
  def mod_inverse(mod)
    self.pow(mod - 2, mod)
  end
end

N = gets.to_i
X = gets.split.map(&:to_i)
S = X.sum
T = S ** 2 - X.map { |x| x ** 2 }.sum
MOD = 10 ** 9 + 7

res = Rational(T, S) + 1
a = res.denominator
b = res.numerator

puts b * a.mod_inverse(MOD) % MOD