1697809domain: NAppears in sequencesE.g.f.: exp(x/(1-2*x))/sqrt(1-4*x^2).at n=7A115326Number of 4Xn 0..1 arrays avoiding 0 0 0 and 0 1 0 horizontally and 0 1 1 and 1 0 1 vertically.at n=9A207731Perfect squares k such that each decimal digit of k is equal to the difference of at least two other digits of k.at n=24A255893