A362708 a(n) is the number of almost unitary polyominoes of size n. An almost unitary polyomino is one in which all but 1 of its perimeter walls have length 1.

0, 0, 0, 1, 0, 0, 2, 2, 1, 6, 9, 11, 21, 49, 69, 117, 249, 427

Offset: 1

Author

John Mason, Apr 30 2023

Keywords

• nonn
• hard
• more

Examples

			a(4)=1 because of:
  O
  OO
  O
		

Links

• George Sicherman, Catalogue of Almost Unitary Polyominoes

Crossrefs

Cf. A245660, A362709.