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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 | class Integer def reverse(a = 0 ) n = self while n > 0 a = a * 10 + n % 10 n /= 10 end return a end def symmetrize(axis = false ) reverse self / (axis ? 10 : 1 ) end def palindrome? self == reverse end def double self * self end end ( 1 .. 10000 ).to_a. each do |i| [ false , true ].map {|axis| i.symmetrize(axis).double }. each {|n| puts n if n <= 10 ** 14 and n.palindrome? } end |