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 A293261 #10 Feb 09 2021 06:40:03 %S A293261 1,5,106,6074,943340,419355340,554485727288,2208574156731474, %T A293261 26609978139626497670,973224195603423767343946, %U A293261 108342096917091380628767818812,36763211016528549310068224122368860,38044287043749436284594644308861499605492 %N A293261 Number of fixed polyominoes without holes that have a width and height of n. %C A293261 Equivalently, the number of cycles on an (n+1) X (n+1) grid that touch each of the four outside edges. %H A293261 Andrey Zabolotskiy, <a href="/A293261/b293261.txt">Table of n, a(n) for n = 1..16</a> %H A293261 Anthony J. Guttmann and Iwan Jensen, <a href="https://doi.org/10.1007/978-1-4020-9927-4_10">Effect of Confinement: Polygons in Strips, Slabs and Rectangles</a>, in: Polygons, Polyominoes and Polycubes, LNP 775, Springer, 2009. See Table 10.2 on p. 239. %Y A293261 Main diagonal of A232103. %Y A293261 Cf. A268404. %K A293261 nonn %O A293261 1,2 %A A293261 _Andrew Howroyd_, Oct 04 2017