OFFSET
0,2
COMMENTS
This sequence counts "free" polyforms where holes are allowed. This means that two polyforms are considered the same if one is a rigid transformation (translation, rotation, reflection or glide reflection) of the other.
LINKS
Peter Kagey, Illustration of a(3) = 7.
George Sicherman, Catalogue of Polybirds.
Wikipedia, Rhombitrihexagonal tiling
CROSSREFS
Analogous for other tilings: A000105 (square), A000228 (hexagonal), A000577 (triangular), A197156 (prismatic pentagonal), A197159 (floret pentagonal), A197459 (rhombille), A197462 (kisrhombille), A197465 (tetrakis square), A309159 (snub square), A343398 (trihexagonal), A343406 (truncated hexagonal), A343577 (truncated square).
KEYWORD
nonn,more,hard
AUTHOR
Peter Kagey, May 11 2021
STATUS
approved