1820448domain: NAppears in sequencesTheta series of laminated lattice LAMBDA_18.at n=4A023940Number of nX6 0..1 arrays avoiding 0 0 0 and 0 1 1 horizontally and 0 0 1 and 1 0 1 vertically.at n=20A207022a(n) = phi( 2^(2*n) + 2^n + 1 ) / (6*n), where phi() is Euler's totient function (A000010).at n=13A376482