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

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, 0, 816, 1136, 0, 0, 3098, 4088, 0, 0, 11711, 14868, 0, 0, 44462, 54526, 0, 0, 169213, 201527, 0, 0, 646441, 750169, 0, 0, 2477819, 2809931, 0, 0, 9530788, 10582370, 0, 0, 36768799, 40043785

Offset

1,13

Comments

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

Links

Table of n, a(n) for n=1..65.

Formula

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

Example

a(12)=1 because of:
   O
   OOOO
   O O
  OOOO
     O

Crossrefs

Cf. A000105, A144553, A234007.

Sequence in context: A244120 A277536 A348849 * A269159 A216394 A028590

Adjacent sequences: A351139 A351140 A351141 * A351143 A351144 A351145

Keyword

nonn,hard

Author

John Mason, Feb 02 2022

Status

approved