OFFSET
1,11
COMMENTS
This sequence enumerates a subset of the polyominoes enumerated by A056878.
EXAMPLE
For a(7)=1, the heptomino with exactly fourfold symmetry and axes of symmetry parallel to the diagonals of the cells is composed of two 2 X 2 squares with one cell in common.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
John Mason, Feb 03 2022
STATUS
approved