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 A219994 #32 Mar 30 2025 10:56:40 %S A219994 1,0,2,8,380,21272,5350806,3238675344,6652506271144,38896105985522272, %T A219994 711716770252031164458,38776997923112110535353528, %U A219994 6460929292946758939597712150496,3245656750963660788826395580466708824,4953412325525289651086730443567098343730966,22873302288206466754758793232467436030071524731072 %N A219994 Number of tilings of an n X n square using dominoes and right trominoes. %H A219994 Alois P. Heinz, <a href="/A219994/b219994.txt">Table of n, a(n) for n = 0..17</a> %H A219994 Kai Liang, <a href="https://arxiv.org/abs/2503.17698">Solving tiling enumeration problems by tensor network contractions</a>, arXiv:2503.17698 [math.CO], 2025. See p. 25, Table 4. %e A219994 a(3) = 8, because there are 8 tilings of a 3 X 3 square using dominoes and right trominoes: %e A219994 .___._. .___._. .___._. .___._. %e A219994 |___| | |___| | |___| | |_. | | %e A219994 | ._|_| | | |_| | |___| | |_|_| %e A219994 |_|___| |_|___| |_|___| |_|___| %e A219994 ._.___. ._.___. ._.___. ._.___. %e A219994 | |___| | | ._| | |___| | |___| %e A219994 |___| | |_|_| | |_|_. | |_| | | %e A219994 |___|_| |___|_| |___|_| |___|_| . %Y A219994 Main diagonal of A219987. %Y A219994 Cf. A233807, A364504. %K A219994 nonn %O A219994 0,3 %A A219994 _Alois P. Heinz_, Dec 02 2012