402653182domain: NAppears in sequencesa(n) = 3*2^n - 2.at n=27A033484a(n) = (n-2)*(n-3)*2^(n-2)+2^n-2.at n=21A217528Number of bisymmetric, quasitrivial, and order-preserving binary operations on the n-element set {1,...,n}.at n=28A296953a(n) = n! * [x^n] (2*x - 4*exp(x) + 3*exp(2*x) + 3) / 2.at n=28A369491