%I #9 Feb 17 2022 06:05:04

%S 0,0,0,0,0,0,0,0,0,0,0,1,2,0,0,3,7,0,0,14,25,0,0,55,90,0,0,216,319,0,

%T 0,816,1136,0,0,3098,4088,0,0,11711,14868,0,0,44462,54526,0,0,169213,

%U 201527,0,0,646441,750169,0,0,2477819,2809931,0,0,9530788,10582370,0,0,36768799,40043785

%N Free chiral polyominoes with n squares, having 90-degree rotational symmetry about the center of a square of the underlying square matrix.

%C The sequence enumerates a subset of the polyominoes enumerated by A144553.

%F For n multiple of 4, a(n) = A144553(n) - A234007(n/4); otherwise a(n) = A144553(n).

%e a(12)=1 because of:

%e O

%e OOOO

%e O O

%e OOOO

%e O

%Y Cf. A000105, A144553, A234007.

%K nonn,hard

%O 1,13

%A _John Mason_, Feb 02 2022