210796144092domain: NAppears in sequencesExpansion of x*( 1+2*x-x^2-6*x^3 ) / ( 1-9*x^2+12*x^4 ).at n=26A176968Start with a single cell at coordinates (0, 0), then iteratively subdivide the grid into 3 X 3 cells and remove the cells whose sum of modulo 2 coordinates is 2; a(n) is the number of cells after n iterations.at n=13A285391