OFFSET
1,3
COMMENTS
A perforated polyomino is a polyomino in which every cell has at least one even coordinate.
EXAMPLE
a(4)=3 because there are 5 tetrominoes, and the skew and square tetrominoes do not lie in the perforated grid, which leaves 3.
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
George Sicherman, Oct 23 2017
EXTENSIONS
a(16) - a(21) from Joerg Arndt, Dec 11 2023
STATUS
approved