Integer#collatz

collatz.rb

class Integer
  def collatz &block
    return to_enum :collatz unless block_given?
    return self if self < 0
    block[self]
    n = self
    until n < 2
      n = n.even? ? n/2 : n*3+1 # <- *1
      block[n]
    end
    self
  end
end
# 3.collatz.to_a
# => [3, 10, 5, 16, 8, 4, 2, 1]
# 27.collatz.count
# => 112