mod([floor(floor(y/k)/2^(k*floor(x)+mod([floor(y),k]))),2])>1/2,x>0,N<y<N+k

k=3,N=k*[2^1+2^3+2^4+2^5+2^7]

Number the pixels in a 3x3 bitmap like this:
2 5 8
1 4 7
0 3 6
Draw a "+'" sign in a 3x3 grid like this:
.*.
***
.*.
The number representing that bitmap is given by N above.
Draw the equation below (by clicking on the "X" and selecting a color) to see the other bitmaps around the "+"

mod([floor(floor(y/k)/2^(k*floor(x)+mod([floor(y),k]))),2])>1/2,x>0,y>0

Graph of the formula

This file was created by Graphing Calculator 3.5.
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