OFFSET
1,8
COMMENTS
This sequence counts free connected (via common edges) polyominoes with given site-perimeter. The site-perimeter of a polyomino is the number of cells that are adjacent to it (via common edges). This sequence allows holes of any kind.
LINKS
John Mason, Examples
EXAMPLE
a(4) = a(6) = a(7) = 1 as the monomino, domino and L-shaped tromino are the only polyominoes with site perimeter 4, 6 and 7 respectively.
a(5) = 0 as no polyomino has a site-perimeter of 5.
a(8) = 5 as the straight tromino, square tetromino, T-tetromino, S-tetromino and cross pentomino are the only polyominoes with site perimeter 8. See link "Examples".
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
John Mason from an idea of Allan C. Wechsler, Oct 10 2023
STATUS
approved