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.
%I A359519 #10 Jan 05 2023 11:04:42 %S A359519 0,0,0,0,0,0,0,1,2,16,70,378,1772,8456,38623,174400,771944,3378937 %N A359519 Number of free polyominoes of n cells with multiply-connected interiors. %F A359519 a(n) = A000105(n) - A342537(n) (all free polyominoes minus simply-connected interior polyominoes). %e A359519 a(8) = 1 because of: %e A359519 OOO %e A359519 O O %e A359519 OOO %Y A359519 Cf. A000104, A000105, A001419, A342537, A359520. %K A359519 nonn,more %O A359519 1,9 %A A359519 _John Mason_, Jan 04 2023