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 A305324 #19 Jun 27 2025 21:58:56 %S A305324 1,1,6,90,3356,232283,27964488 %N A305324 Number of one-sided 'divisible' polyominoes of size 2^(n-1), where a 'divisible' polyomino is either a monomino (square) or a polyomino which can be separated into two identical 'divisible' polyominoes. %C A305324 a(n) is nonzero for any n >= 1. Proof is trivial by induction. %C A305324 a(n) <= A000988(2^(n-1)) as any polyomino counted here is also counted in A000988. %e A305324 For n = 3 (polyominoes of size 4), the 'divisible' polyominoes are the I, O, J, L, S and Z tetrominoes. The T tetromino is not 'divisible'. %Y A305324 Cf. A000988. %K A305324 nonn,more %O A305324 1,3 %A A305324 _Josh Marza_, May 30 2018 %E A305324 Definition changed and more terms added by _John Mason_, Sep 20 2022