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What is the maximum number of queens that can be placed on a standard 8x8 chessboard such that no one of them is capable of attacking any of the others in a single move?

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8.

Because:

Obviously, you can't have more than 8, since you would have a row (and column) with more than one queen on it.

According to Wolfram-Alpha, there are

12 unique solutions, plus an additional 80 solutions from rotation/reflection.

One possible solution is:

8 Queens not attacking each other.  Image from codereview.stackexchange.com

A list (and images!) of all

12 base solutions can be found both at the above Wolfram-Alpha link and Wikipedia. (Thank you Kevin for the link).

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Sorry for reviving a 5 years old question, but I can fit:

16 queens

I hope to avoid downvotes by pointing out that this troll solution satisfies all the conditions of the original question.

(enter image description here

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    $\begingroup$ Is there really a point to necroing a 5 year old question with a response you openly acknowledge is a troll answer that clearly doesn't address the intent of the question? Please don't. $\endgroup$ – Rubio Jun 15 at 21:59
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    $\begingroup$ A troll solution is still a solution. Take it as an oportunity to see the importance of a good design in puzzle creation and an example of thinking out of the box. $\endgroup$ – Daniel Duque Jun 15 at 23:48
  • $\begingroup$ Just missing to approve that it is the maximal solution.(+1) $\endgroup$ – z100 Jun 16 at 20:15

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