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A034185 Number of symmetric n X 3 crossword puzzle grids. 3
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified April 14 16:31 EDT 2021. Contains 342949 sequences. (Running on oeis4.)