A131487 - OEIS

A131487

a(n) is the number of polyominoes with n edges, including inner edges.

0, 0, 0, 1, 0, 0, 1, 0, 0, 2, 0, 1, 4, 0, 1, 11, 1, 7, 27, 4, 21, 85, 21, 92, 264, 89, 345, 914, 394, 1405, 3155, 1736, 5530, 11400, 7586, 22022, 41756, 32702, 87158, 156412, 139253, 346836, 592661, 589101, 1379837, 2275935, 2476770, 5501846, 8830267, 10363627, 21970992, 34594887, 43188260, 87950618

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OFFSET

1,10

COMMENTS

An n-celled polyomino with perimeter p has (4n+p)/2 edges. The maximum number of edges in an n-celled polyomino is 3n+1.

LINKS

Table of n, a(n) for n=1..54.

Andrew Clarke, Isoperimetrical Polyominoes

FORMULA

See A342243 for formula.

EXAMPLE

A single cell has 4 edges; a domino has 7 edges (this includes the edge between the two cells); both trominoes have 10 edges; their possible orientations are not considered distinct. Thus a(4) = a(7) = 1, a(10) = 2, and a(n) = 0 for n < 10 not equal to 4 or 7.

a(22) = 85 = 83 + 2: there are 83 polyominoes with 7 cells and perimeter 16 (such as a 1 X 7 strip) and two polyominoes with 8 cells and perimeter 12 (a 3 X 3 square without a corner and a 4 X 2 rectangle), and each of these polyominoes has 22 edges.

a(23) = 21. a(24) = 91+1. a(25) = 255+9. a(26) = 89. a(27) = 339+6. a(28) = 847+67. a(34) = 9734+1655+11. a(35) = 7412+174. - R. J. Mathar, Feb 22 2021

CROSSREFS

Cf. A000105, A057730, A342243.

Cf. A131482 (number of n-celled polyominoes with perimeter 2n+2), A131488 (analog for hexagonal tiling).

Sequence in context: A307177 A340264 A291878 * A230747 A308628 A181670

Adjacent sequences: A131484 A131485 A131486 * A131488 A131489 A131490

KEYWORD

hard,nonn

AUTHOR

Tanya Khovanova, Jul 28 2007

EXTENSIONS

a(23)-a(35) from R. J. Mathar, Feb 22 2021

a(36)-a(39) from R. J. Mathar, Mar 11 2021

a(40)-a(44) from R. J. Mathar, Mar 24 2021

a(45)-a(54) from John Mason, Apr 28 2023

STATUS

approved