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 A233320 #43 Mar 25 2025 12:17:09 %S A233320 1,1,1,1,0,1,1,0,0,1,1,1,0,1,1,1,0,3,3,0,1,1,0,0,10,0,0,1,1,1,0,23,23, %T A233320 0,1,1,1,0,11,62,0,62,11,0,1,1,0,0,170,0,0,170,0,0,1,1,1,0,441,939,0, %U A233320 939,441,0,1,1,1,0,41,1173,0,8342,8342,0,1173,41,0,1 %N A233320 Number A(n,k) of tilings of a k X n rectangle using trominoes of any shape; square array A(n,k), n>=0, k>=0, read by antidiagonals. %C A233320 Every row and column satisfies a linear recurrence. - _Peter Kagey_, Jul 17 2019 %H A233320 Liang Kai, <a href="/A233320/b233320.txt">Antidiagonals n = 0..35, flattened</a> (Antidiagonals 0..28 from Alois P. Heinz) %H A233320 Wikipedia, <a href="https://en.wikipedia.org/wiki/Tromino">Tromino</a> %F A233320 A(n,k) = 0 <=> n*k mod 3 > 0. %e A233320 Square array A(n,k) begins: %e A233320 1, 1, 1, 1, 1, 1, 1, ... %e A233320 1, 0, 0, 1, 0, 0, 1, ... %e A233320 1, 0, 0, 3, 0, 0, 11, ... %e A233320 1, 1, 3, 10, 23, 62, 170, ... %e A233320 1, 0, 0, 23, 0, 0, 939, ... %e A233320 1, 0, 0, 62, 0, 0, 8342, ... %e A233320 1, 1, 11, 170, 939, 8342, 80092, ... %e A233320 1, 0, 0, 441, 0, 0, 614581, ... %e A233320 1, 0, 0, 1173, 0, 0, 5271923, ... %Y A233320 Columns (or rows) include: A000012, A001835, A134438, A233339, A233340, A233290, A233343, A269958, A215826, A269959, A269664. %Y A233320 Cf. A099390, A230031, A233427, A270061, A364457. %K A233320 nonn,tabl %O A233320 0,18 %A A233320 _Alois P. Heinz_, Dec 07 2013