18596183472domain: NAppears in sequencesOne quarter the number of nX3 1..4 arrays with no two neighbors of any element equal to each other.at n=18A183355Number of 3Xn binary arrays without the pattern 0 1 diagonally or antidiagonally.at n=20A188825a(1) = 1, a(2) = 2, a(3) = 5; thereafter a(n) = 2 * Sum_{k=1..n-1} a(k).at n=22A257970