A362709 a(n) is the number of almost almost unitary polyominoes of size n. An almost almost unitary polyomino is one in which all but 2 of its perimeter walls have length 1.

0, 1, 2, 2, 4, 12, 15, 29, 58, 116, 199, 403, 790, 1509, 2857, 5700, 10941, 21032

Offset

1,3

Links

Table of n, a(n) for n=1..18.

George Sicherman, Catalogue of Almost Almost Unitary Polyominoes

Example

a(4)=2 because of:
  O  O
  O  OO
  O   O
  O

Crossrefs

Cf. A245660, A362708.

Sequence in context: A353131 A134435 A136718 * A112362 A134720 A019225

Adjacent sequences: A362706 A362707 A362708 * A362710 A362711 A362712

Keyword

nonn,hard,more

Author

John Mason, Apr 30 2023

Status

approved