KNOWN_ARMSTRONG = [
  1,
  2,
  3,
  4,
  5,
  6,
  7,
  8,
  9,
  153,
  370,
  371,
  407,
  1634,
  8208,
  9474,
  54748,
  92727,
  93084,
  548834,
  1741725,
  4210818,
  9800817,
  9926315,
  24678050,
  24678051,
  88593477,
  146511208,
  472335975,
  534494836,
  912985153,
  4679307774,
  32164049650,
  32164049651,
  40028394225,
  42678290603,
  44708635679,
  49388550606,
  82693916578,
  94204591914,
  28116440335967,
  4338281769391370,
  4338281769391371,
  21897142587612075,
  35641594208964132,
  35875699062250035,
  1517841543307505039,
  3289582984443187032,
  4498128791164624869,
  4929273885928088826,
  63105425988599693916,
  128468643043731391252,
  449177399146038697307,
  21887696841122916288858,
  27879694893054074471405,
  27907865009977052567814,
  28361281321319229463398,
  35452590104031691935943,
  174088005938065293023722,
  188451485447897896036875,
  239313664430041569350093,
  1550475334214501539088894,
  1553242162893771850669378,
  3706907995955475988644380,
  3706907995955475988644381,
  4422095118095899619457938,
  121204998563613372405438066,
  121270696006801314328439376,
  128851796696487777842012787,
  174650464499531377631639254,
  177265453171792792366489765,
  14607640612971980372614873089,
  19008174136254279995012734740,
  19008174136254279995012734741,
  23866716435523975980390369295,
  1145037275765491025924292050346,
  1927890457142960697580636236639,
  2309092682616190307509695338915,
  17333509997782249308725103962772,
  186709961001538790100634132976990,
  186709961001538790100634132976991,
  1122763285329372541592822900204593,
  12639369517103790328947807201478392,
  12679937780272278566303885594196922,
  1219167219625434121569735803609966019,
  12815792078366059955099770545296129367,
  115132219018763992565095597973971522400,
  115132219018763992565095597973971522401
]

class Integer
  def is_armstrong?
    digits = self.to_s.chars.map(&:to_i)
    self == digits.map{_1**digits.count}.inject(&:+)
  end
end

def test
  numbers = KNOWN_ARMSTRONG
  KNOWN_ARMSTRONG.count.times{numbers << rand(KNOWN_ARMSTRONG.last)}
  numbers.sort.each do |x|
    puts "#{x} is #{'not ' unless x.is_armstrong?}an Armstrong number"
  end
end

test