Superpermutation
A superpermutation is a string that contains every permutation of a given set of n symbols as a contiguous substring. Finding the shortest possible superpermutation is a problem in Combinatorics.
In 2011, a 4chan user trying to watch anime 'The Melancholy of Haruhi Suzumiya' in every episode order accidentally proved the lower bound of superpermutations, an unsolved mathematics problem. The proof went unnoticed for 7 years.
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