A359519 Number of free polyominoes of n cells with multiply-connected interiors.
0, 0, 0, 0, 0, 0, 0, 1, 2, 16, 70, 378, 1772, 8456, 38623, 174400, 771944, 3378937
Offset: 1
Examples
a(8) = 1 because of: OOO O O OOO
This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
a(8) = 1 because of: OOO O O OOO