OFFSET
1,2
COMMENTS
Half of the cells lie on each side of the axis of symmetry, so there must be an even number. This is one of three sequences used to calculate A030223, the number of achiral polyominoes for this tiling. Two fixed polyominoes are identical only if one is a translation of the other.
EXAMPLE
These are halves above the axis of symmetry of the polyominoes for n<4. The bottom edge of each is the axis of symmetry.
/\ /\
____ ____ ________ ____ /__\ /__\
/\ /\ / \ /\ \ /\ / /\ /\ /\ / \ /\
/__\ /__\/ \/__\ \/__\/ /__\/__\ /__\/ \/__\
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert A. Russell, Jul 26 2023
STATUS
approved