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

Author

John Mason, Feb 06 2023

Keywords

• nonn

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.

Examples

			a(4)=1 because of:
  OO
 OO
		

Links

• Andrew Howroyd, Table of n, a(n) for n = 1..1000
• Andrew Howroyd, Formula and PARI Program, 2023.
• John Mason, Examples

Crossrefs

Cf. A028247, A270060, A360419, A360421.

Programs

PARI

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

Formula

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

Extensions

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