|
|
A255539
|
|
Number of digital images in Z^2 with 4-adjacency on n points up to isomorphism.
|
|
2
|
|
|
1, 1, 1, 3, 4, 10, 19, 51, 112, 300, 746, 2042, 5450, 15197, 42192, 119561, 339594
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,4
|
|
COMMENTS
|
Also the number of polyominoes on n points, up to isomorphism of the adjacency graph.
Also the number of "grid graphs" (finite induced subgraphs of the integer lattice using only horizontal and vertical edges) on n vertices.
|
|
LINKS
|
|
|
EXAMPLE
|
a(4) = 3: (1) the square tetromino has the 4-cycle as its "adjacency graph"; (2) the T-tetromino corresponds to the claw graph; (3) the straight, skew, and L-tetromino all correspond to the 4-path.
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,more,hard
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|