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 A219874 #29 Mar 30 2025 10:54:31 %S A219874 1,0,2,14,184,9612,1143834,354859954,295743829064,631206895803116, %T A219874 3541054185616706122,51821077154605344550820, %U A219874 1976225122734369352127065686,196913655491597719598898811003348,51179690353659852099434654264900753288,34716223657627061096793572212632925410608268 %N A219874 Number of tilings of an n X n square using dominoes and straight (3 X 1) trominoes. %H A219874 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 A219874 a(3) = 14, because there are 14 tilings of a 3 X 3 square using dominoes and straight (3 X 1) trominoes: %e A219874 ._____. ._____. ._____. ._____. .___._. .___._. .___._. %e A219874 | | | | | | | | | |___| | |___| | | | | |___| | |___| | %e A219874 | | | | | |_|_| | |___| | | | | |_|_| | |___| | | | | | %e A219874 |_|_|_| |_|___| |_|___| |_|_|_| |___|_| |___|_| |_|_|_| %e A219874 ._____. ._____. ._____. ._____. ._____. ._____. ._____. %e A219874 |_____| |_____| |_____| |_____| | |___| | | | | |___| | %e A219874 |_____| | |___| | | | | |___| | |_|___| |_|_|_| |___|_| %e A219874 |_____| |_|___| |_|_|_| |___|_| |_____| |_____| |_____| . %Y A219874 Main diagonal of A219866. %Y A219874 Cf. A233807, A364504. %K A219874 nonn %O A219874 0,3 %A A219874 _Alois P. Heinz_, Nov 30 2012 %E A219874 a(12) from _Alois P. Heinz_, Sep 30 2014 %E A219874 a(13)-a(15) (using _Liang Kai_'s terms in A219866) from _Alois P. Heinz_, Mar 12 2025