Permutation
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In mathematics, a permutation of a set can mean one of two different things:an arrangement of its members in a sequence or linear order, or
the act or process of changing the linear order of an ordered set.
In the 15 puzzle the goal is to get the squares in ascending order. Initial positions which have an odd number of inversions are impossible to solve.
Anagram
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An anagram is a word or phrase formed by rearranging the letters of a different word or phrase, typically using all the original letters exactly once. For example, the word anagram itself can be rearranged into nag a ram; which is an Easter egg in Google when searching for the word "anagram".
The game of Boggle