OFFSET
2,3
COMMENTS
For any polygon, build a bracelet of black and white beads by following the border of the polygon in a clockwise direction, adding a black bead for each right-turning right angle, and a white bead for each left-turning right angle. The polygons counted by this sequence are those whose bracelets have all the black beads together and all the white beads together.
LINKS
EXAMPLE
a(4)=3, as there are 3 self-avoiding polygons (SAPs) of perimeter 8 that satisfy the condition; these are the polygons corresponding to the strip and L-shaped trominoes, and the square tetromino.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
John Mason, Allan C. Wechsler, Mar 15 2021
STATUS
approved