Enigma 1188: Square roundabout
21 December 2015
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From New Scientist #2344, 25th May 2002 [link]
I was playing about with my seven-digit-display calculator, showing my numerate nephew a trick or two. I displayed a number on the calculator and he looked at it upside down. After some jottings of his own he declared “I can see a number too, and it’s a perfect square”.
I then doubled my original number and displayed the answer and again he looked at it upside down and did some calculations.
“I can still see a number, and it’s another perfect square”, he said.
Which number did I originally display?