Created a method to return the Collatz Sequence for a given n, then created a method to find the number with the longest Collatz Sqeuence between 1 and n

collatz.rb

def collatz(n)
  # set an empty arry to contain the values of the sequence
  ary = []
  # set initial index value to 0
  index = 0

  # start by pushing n into the array
  ary.push(n)
  # loop until the array includes the number 1, i.e. until the sequence is complete
  until ary.include?(1)
    # if the most recent number in the array is even, push a new value (half its value) into the array
    if ary[index] % 2 == 0
      ary.push(ary[index] / 2)
    # if the most recent number is odd, push a new value (3 times its value + 1) into the array
    elsif ary[index] % 2 == 1
      ary.push(ary[index] * 3 + 1)
    end
    # increment the index value by 1 each loop
    index += 1
  end
  return ary.inspect
end

def longest_collatz(n)
  longest_n = 0
  number_to_test = 1
  while number_to_test <= n
    if collatz(number_to_test).length > longest_n
      longest_n = number_to_test
      number_to_test += 1
    else
      number_to_test += 1
    end
  end
  return longest_n
end


puts collatz(3)
puts collatz(4)
puts collatz(7)

puts longest_collatz(1000000)