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Programming Enigma Puzzles

12 February 2012

Posted by on **From New Scientist #2737, 5th December 2009** [link]

4 April 2001 was the first doubly square date of the century because whether written in the order

day.month.yearor in the ordermonth.day.year(in each instance with two digits for each element) it comes out as 04.04.01, and 40401 is 201^{2}.Still with two digits for each element, there are some doubly square dates for which the square that comes from the order

day.month.yearis not the same as the square that comes from the ordermonth.day.year. This is the case for each of the next two doubly square dates after 4 April 2001. What are those two dates (in the same form as 4 April 2001)?

[enigma1574]

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The following Python program runs in 50ms.

Solution:The dates are 12 April 2009 and 4 December 2009.