n = gets.not_nil!.to_i
a = gets.not_nil!.split.map(&.to_i)
ma = a.max * 2
ans = 0

(1..ma).each do |num|
  dic = Hash(Int32, Int32).new(0)
  limit = Math.min(ma // num + 1, n)
  
  (0...limit).each do |i|
    d = a[i] - num * (i + 1)
    ans += dic[-d]
    dic[d] += 1
  end
end

puts ans