226300domain: NAppears in sequencesNumber of 4 X n 0..1 arrays avoiding 0 0 1 and 1 0 1 horizontally and 0 1 0 and 1 0 1 vertically.at n=19A207255G.f. A(x) satisfies: the sum of the coefficients of x^k, k=0..n, in A(x)^n equals (3*n)!/n!^3, which is de Bruijn's sequence S(3,n) (A006480), for n>=0.at n=6A232683