A352720 a(n) is the number of free polyominoes of width 2 and size n.

1, 1, 4, 5, 12, 18, 37, 60, 117, 200, 379, 669, 1250, 2247, 4168, 7570, 13987, 25549, 47108, 86319, 158978, 291806, 537105, 986786, 1815699, 3337560, 6140047, 11289571, 20767180, 38189927, 70246680, 129191148, 237627757, 437042337, 803861244, 1478488577, 2719392160, 5001663330, 9199544069

Offset: 2

Author

John Mason, Mar 31 2022

Keywords

• nonn

Examples

			There is one polyomino, the domino, of width 2 and size 2. So a(2) = 1.
There is one tromino, L-shaped, of width 2. So a(3) = 1.
		

Links

• John Mason, Table of n, a(n) for n = 2..1000
• John Mason, Java program
• John Mason, Explanation of formulas
• R. J. Mathar, Corrigendum to "polyomino enumeration results" (Parkin et al), vixra:1905.0474 (2019) Table 1 column 2.

Crossrefs

Cf. A000105, A335711, A353067.

Formula

For a set of recursive formulas to generate a(n), see the link for the Java program extract.