A034185 Number of symmetric n X 3 crossword puzzle grids.

1, 3, 11, 21, 61, 111, 309, 565, 1563, 2859, 7907, 14459, 39991, 73117, 202227, 369729, 1022587, 1869581, 5170829, 9453757, 26146909, 47804041, 132214959, 241726811, 668560673, 1222320359, 3380656559, 6180808253, 17094691953, 31253992007, 86441342981

Offset

1,2

Comments

Rules: all white squares are edge connected; at least 1 white square on every edge of grid; symmetric ones have 180-degree rotational symmetry.

Links

Table of n, a(n) for n=1..31.

Sean A. Irvine, Java program (github)

Crossrefs

Cf. A001333, A034184, A034186, A034187.

Sequence in context: A147073 A147191 A327607 * A184053 A240371 A158653

Adjacent sequences: A034182 A034183 A034184 * A034186 A034187 A034188

Keyword

nonn

Author

Erich Friedman

Extensions

a(23)-a(31) from Sean A. Irvine, Aug 07 2020

Status

approved