Friday, 10 July 2015

mathematics - Neighbouring numbers summing to a prime on a 3x3


Can you place distinct numbers from 0 to 9 on a 3x3 grid such that every pair of neighbouring (horizontally and vertically) numbers sum to a prime? Can you find multiple solutions? Note that the placed numbers can only be used once and one number will remain unused. The generated primes can be reused.


Good luck!



Answer



The answer is:



Yes



Explanation:





650
123
498

Where the generated primes in the rows are 11, 5, 3, 5, 13, 17 respectively, and in the columns 7, 5, 7, 11, 3 and 11.

Further:



You can generate multiple solutions from reflecting and rotating this grid. I don't know if you can make any more solutions which are fundamentally different from this, though I haven't tried.




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