A360420 a(n) = the number of Z-frame polyominoes with n cells, reduced for symmetry.

0, 0, 0, 1, 2, 6, 10, 19, 27, 43, 58, 85, 105, 143, 175, 226, 266, 334, 386, 475, 534, 641, 717, 854, 933, 1092, 1187, 1385, 1482, 1713, 1820, 2091, 2203, 2511, 2637, 2998, 3110, 3516, 3647, 4118, 4226, 4761, 4865, 5461, 5576, 6221, 6319, 7088, 7138, 7953

Offset

1,5

Comments

A Z-frame polyomino has a perimeter that forms a self-avoiding polygon such that as you traverse the perimeter counterclockwise you encounter turns in the order LLLRLLLR.

Links

Andrew Howroyd, Table of n, a(n) for n = 1..1000

Andrew Howroyd, Formula and PARI Program, 2023.

John Mason, Examples

Formula

a(n) <= A028247(n). - Andrew Howroyd, Feb 08 2023

Example

a(4)=1 because of:
  OO
 OO

Prog

(PARI) seq(50) \\ See Links - Andrew Howroyd, Feb 08 2023

Crossrefs

Cf. A028247, A270060, A360419, A360421.

Sequence in context: A370048 A054273 A127567 * A169643 A005993 A028247

Adjacent sequences: A360417 A360418 A360419 * A360421 A360422 A360423

Keyword

nonn

Author

John Mason, Feb 06 2023

Extensions

Terms a(19) and beyond from Andrew Howroyd, Feb 08 2023

Status

approved