describe Integer, "#dodecagonal?" do
  
  # A051624
  DODECAGONAL = [0,1,12,33,64,105,156,217,288,369,460,561,672,793,
                 924,1065,1216,1377,1548,1729,1920,2121,2332,2553,
                 2784,3025,3276,3537,3808,4089,4380,4681,4992,5313,
                 5644,5985,6336,6697,7068,7449,7840,8241,8652]

  it "returns true for dodecagonal numbers" do
    DODECAGONAL.each{|n| n.should be_dodecagonal}
  end

  it "returns false for non-dodecagonal numbers" do
    ((0..DODECAGONAL.last).to_a - DODECAGONAL).each do |n| 
      n.should_not be_dodecagonal
    end
  end
end