400800400domain: NAppears in sequencesSquares of the form u'v'w, where in decimal representation u=n^2, v=2*n^2 and w=n^2 possibly with a leading zero.at n=19A077432Squares containing only the digits 0, 4 or 8.at n=17A202172Number of 6Xn 0..1 arrays avoiding 0 0 1 and 0 1 1 horizontally and 0 0 1 and 1 0 1 vertically.at n=17A208145