Enumeration of 3- and 4-Wilf classes of four 4-letter patterns
David Callan, Toufik Mansour ยท Notes on Number Theory and Discrete Mathematics ยท 2018
Let ๐ ๐ be the symmetric group of all permutations of ๐ letters.We show that there are precisely 27 (respectively, 15) Wilf classes consisting of exactly 3 (respectively, 4) symmetry classes of subsets of four 4-letter patterns.