combinations.rb

require 'set'
require 'prime'

letters = 3
max_word_length = 5

alphabet = (0...letters).collect { |i| ('A'.ord + i).chr }
all_words = SortedSet.new

for i in 1..max_word_length
  words = SortedSet.new

  slice_limit = i.prime? ? 1 : i / 2

  alphabet.repeated_permutation(i).map {|permutation| permutation.join}.each do |word|
    skip = false
    double_word = (word * 2)

    (0...i).collect { |j| double_word[j, i] }.each do |rotation|
      skip = true if words.include? rotation
      unless skip 
        for k in 1..slice_limit
          skip = true if i % k == 0 && rotation.chars.each_slice(k).map(&:join).uniq.size == 1
          break if skip
        end
      end
      break if skip
    end
    words.add(word) unless skip
  end

  words.each { |word| puts word }
  all_words += words
end