Generate letters to represent number using ruby?

Question

I would like to generate a sequence of letters i.e. \"A\", \"DE\" \"GJE\", etc. that correspond to a number. The first 26 are pretty easy so 3 returns \"C\", 26 returns \"Z\

Answer 1

Based on sawa's answer, I wanted a method that worked independently, albeit recursively, to achieve the desired outcome:

def num_to_col(num)
  raise("invalid value #{num} for num") unless num > 0
  result, remainder = num.divmod(26)
  if remainder == 0
    result -= 1
    remainder = 26
  end
  final_letter = ('a'..'z').to_a[remainder-1]
  result > 0 ? previous_letters = num_to_col(result) : previous_letters = ''
  "#{previous_letters}#{final_letter}".upcase
end