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i) Hidden in this 8 x 8 board are the first 31 primes starting with 2 and up to to 127. They occupy adjacent, non-overlapping cells (up to 3), and are read horizontally (from left to right) or vertically (from top to bottom). Find them!

ii) Prepare a similar soup, but in a 10 x 10 board filled with the first 43 primes (2 to 191) such that these primes can be located uniquely inside the soup. Make it as hard as possible to identify primes!

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  • 3
    $\begingroup$ This sounds like it should really be two separate questions $\endgroup$
    – fljx
    Aug 13, 2023 at 16:16
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    $\begingroup$ Question 2 isn't too well defined, mainly because it's impossible to quantify how 'hard' puzzles are. Largest number of red herrings? $\endgroup$ Aug 13, 2023 at 20:57

1 Answer 1

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i)

You can look at the 0's in the grid to uniquely identify 101, 103, 107, 109. That gives us a good starting point and you can continue from the immediate surroundings to fill up the rest of the grid.

ii)

Starting from the original grid and tweaking it a bit:

 1138829711
 1113961178
 9794167291
 1109174711
 2771033155
 7310753317
 1019233159
 1377163543
 3173139191
 1149167137
 

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