28512000domain: NAppears in sequencesCommuting elements: number of ordered pairs g, h in the group GL(2,Z_n) such that gh = hg.at n=21A070943Number of leading even entries in all permutations of {1,2,...,n}.at n=10A152665Triangle of numbers of squares {i^2}, i = 0,1..ceiling(n/2), in permutations of {1..n} in A293857.at n=49A293783