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
Examples
a(4)=2 because of: O O O OO O O O
Links
- George Sicherman, Catalogue of Almost Almost Unitary Polyominoes