|
|
A351190
|
|
Number of polyominoes of n cells with both horizontal and vertical symmetries, for which the 180-degree rotational symmetry has an axis that coincides with the center of a square, but without 90-degree rotational symmetry.
|
|
3
|
|
|
0, 0, 1, 0, 1, 0, 3, 0, 4, 1, 10, 3, 17, 6, 35, 15, 64, 31, 128, 74, 241, 145, 476, 332, 912, 649, 1789, 1446, 3456, 2821, 6779, 6164, 13161, 12049, 25839, 25981, 50348, 50844, 98957, 108514, 193375, 212766, 380522, 450568, 745248, 884843, 1468202, 1862065, 2880780, 3662652, 5681501, 7668922
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,7
|
|
COMMENTS
|
This sequence enumerates a subset of the polyominoes enumerated by A056877.
|
|
LINKS
|
|
|
EXAMPLE
|
a(3)=1 because of the straight tromino.
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|