92819domain: NAppears in sequencesLength of the longest perfect parity pattern with n columns.at n=43A118141Expansion of g.f. (3 -x +2*x^2)/(1 -3*x +2*x^2 -x^3).at n=12A136305a(n) = a(n-2) + a(n-3) for n >= 3, with a(0) = a(1) = 2, a(2) = 1.at n=40A276477