Puzzles that use number properties such as even and odd, multiples of numbers, part of a well-known sequence (i.e. Fibonacci) or theorem (Pythagorean relations) or others in part of the method to solve the question.
Puzzles that require the knowledge and use of number properties to arrive at the solution should use this tag. An example question would be one that has the solver recognize number properties to find odd ones out or the pattern of a sequence. Another way to incorporate number properties into a question is to set up an equation to appear to be regular decimal numbers that is only true if you consider the numbers in a different way (such as using other bases than 10, considering values in degrees or radians, etc.).