6621615domain: NAppears in sequencesNumber of inversions in all fixed-point-free involutions of {1,2,...,2n}.at n=7A161124A Galton triangle: T(n,k) = (2k-1)*(T(n-1,k) + T(n-1,k-1)): a type B analog of the ordered Bell numbers A019538.at n=34A186695