http://nabetani.sakura.ne.jp/hena/ord17scheherazade/

hoge.rb

module Hena
  module Ord17Scheherazade

    # 17301, 100 => [1, 73, 1]
    def self.hoge(i, base)
      fail if i < 0

      result = []
      while i > 0
        i, j = i.divmod base
        result.unshift j
      end

      result
    end

    # 17301
    # =>
    # {
    #   2 => [1, 0, 0, 0, 0, 1, 1, 1, 0, 0, 1, 0, 1, 0, 1],
    #   ...
    #   100 => [1, 73, 1],
    #   ...
    #   17300 => [1, 1],
    # }
    def self.fuga(i)
      return {} if i < 2

      result = {}
      (2..(i - 1)).each do |base|
        result[base] = hoge(i, base)
      end

      result
    end

    def self.piyo(i)
      h = fuga i
      result = []
      h.each do |k, v|
        result << k if v.kaibun?
      end
      return "-" if result.empty?
      result.join ","
    end
  end
end

class Array
  def kaibun?
    self == self.reverse
  end
end

#i = 17301
#p Hena::Ord17Scheherazade.hoge(i, 2)
#p Hena::Ord17Scheherazade.fuga(i)
#p Hena::Ord17Scheherazade.piyo(i)
#p Hena::Ord17Scheherazade.piyo(2)

hoge_spec.rb

require "./hoge.rb"

ANSWERS = [
  [17301, "5,38,100,218,236,5766,17300"],
  [2, "-"],
  [1, "-"],
  [3, "2"],
  [4, "3"],
  [5, "2,4"],
  [6, "5"],
  [10, "3,4,9"],
  [101, "10,100"],
  [1001, "10,25,76,90,142,1000"],
  [10001, "10,24,30,42,80,100,136,10000"],
  [1212, "22,100,201,302,403,605,1211"],
  [123412, "62,100,205,215,30852,61705,123411"],
  [5179, "5178"],
  [4919, "4918"],
  [5791, "5790"],
  [5498, "2748,5497"],
  [453, "150,452"],
  [134, "66,133"],
  [8489, "27,652,8488"],
  [1234, "22,616,1233"],
  [5497, "41,238,5496"],
  [4763, "19,35,432,4762"],
  [3974, "17,27,1986,3973"],
  [3521, "44,55,502,3520"],
  [5513, "20,38,53,148,5512"],
  [8042, "23,29,60,4020,8041"],
  [7442, "37,60,121,3720,7441"],
  [4857, "25,1618,4856"],
  [22843, "49,69,91,141,430,22842"],
  [194823, "84,121,21646,64940,194822"],
  [435697, "160,169,235,626,1822,435696"],
  [142, "3,7,70,141"],
  [886, "5,14,442,885"],
  [3102, "7,65,93,140,281,516,1033,1550,3101"],
  [17326, "11,28,99,105,8662,17325"],
  [32982, "13,72,238,477,716,1433,5496,10993,16490,32981"],
  [36, "5,8,11,17,35"],
  [37, "6,36"],
  [251, "8,250"],
  [252, "5,10,17,20,27,35,41,62,83,125,251"],
  [253, "12,14,22,252"],
  [6643, "2,3,9,81,90,510,948,6642"],
  [5040, "71,79,83,89,104,111,119,125,139,143,167,179,209,239,251,279,314,335,359,419,503,559,629,719,839,1007,1259,1679,2519,5039"],
  [9240, "23,38,62,104,109,119,131,139,153,164,167,209,219,230,263,279,307,329,384,419,439,461,615,659,769,839,923,1154,1319,1539,1847,2309,3079,4619,9239"],
]

describe Hena::Ord17Scheherazade do
  ANSWERS.each do |ans|
    it do
      Hena::Ord17Scheherazade.piyo(ans[0]).should eq(ans[1])
    end
  end
end