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 A263425 #12 Mar 26 2025 16:35:06 %S A263425 1,1,117,178939,19077209438,72713560548906621, %T A263425 13664822582333502156627512 %N A263425 Number of tilings of an 2n X 2n square using tetrominoes of any shape. %H A263425 S. Butler, J. Ekstrand, S. Osborne, <a href="/A230031/a230031.pdf">TETRIS Tiling</a>, AMS Spring Central Sectional, Iowa State University, April 27-28 2013 %H A263425 R. S. Harris, <a href="http://www.bumblebeagle.org/polyominoes/tilingcounting">Counting Polyomino Tilings</a> %H A263425 Wikipedia, <a href="https://en.wikipedia.org/wiki/Tetromino">Tetromino</a> %F A263425 a(n) = A230031(2n,2n). %Y A263425 Bisection (even part) of main diagonal of A230031. %Y A263425 Cf. A004003. %K A263425 nonn,more %O A263425 0,3 %A A263425 _Alois P. Heinz_, Oct 17 2015 %E A263425 a(6) (using terms from A230031) from _Alois P. Heinz_, Mar 26 2025