cp's OEIS Frontend

A351142 Free chiral polyominoes with n squares, having 90-degree rotational symmetry about the center of a square of the underlying square matrix.

%I A351142 #9 Feb 17 2022 06:05:04
%S A351142 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 A351142 0,816,1136,0,0,3098,4088,0,0,11711,14868,0,0,44462,54526,0,0,169213,
%U A351142 201527,0,0,646441,750169,0,0,2477819,2809931,0,0,9530788,10582370,0,0,36768799,40043785
%N A351142 Free chiral polyominoes with n squares, having 90-degree rotational symmetry about the center of a square of the underlying square matrix.
%C A351142 The sequence enumerates a subset of the polyominoes enumerated by A144553.
%F A351142 For n multiple of 4, a(n) = A144553(n) - A234007(n/4); otherwise a(n) = A144553(n).
%e A351142 a(12)=1 because of:
%e A351142    O
%e A351142    OOOO
%e A351142    O O
%e A351142   OOOO
%e A351142      O
%Y A351142 Cf. A000105, A144553, A234007.
%K A351142 nonn,hard
%O A351142 1,13
%A A351142 _John Mason_, Feb 02 2022