n = gets.to_i
a = gets.split.map(&:to_i)
ans = 0
max_a = a.max
0.upto(max_a) do |k|
  dp = Array.new(4) { Array.new(max_a+1, 0) }
  n.times do |i|
    if a[i]-k-1 >= 0 
      dp[3][a[i]] += dp[2][a[i]-k-1]
    end
    if a[i]+k <= max_a
      dp[2][a[i]] += dp[1][a[i]+k]
    end
    if a[i]-k-10 >= 0
      dp[1][a[i]] += dp[0][a[i]-k-10]
    end
    dp[0][a[i]] += 1
  end
  ans += dp[3].sum
end
puts ans