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 A357516 #29 Feb 28 2023 13:07:11 %S A357516 1,2,6,20,2,64,44,512,28,4,64,520,480,6720,43232,14400 %N A357516 Number of snake-like polyominoes in an n X n square that start at the NW corner and end at the SE corner and have the maximum length. %C A357516 The maximum length is given by A357234(n). %C A357516 If the lower bounds of A357234(n) are tight, then a(14)-a(19) are 6720, 43232, 14400, 226560, 1646080, 403712. %C A357516 For n > 1, a(n) is even since for every solution there is also the symmetrical solution reflected in the main diagonal. %H A357516 Yi Yang, <a href="https://bbs.emath.ac.cn/thread-18542-4-1.html">The longest road in a square grid</a> (see 2nd post with a C++ program that generates a(2)-a(19)). %e A357516 For n = 5, there are 2 such snakes shown as follows: %e A357516 X . X X X X X X X X %e A357516 X . X . X . . . . X %e A357516 X . X . X X X X X X %e A357516 X . X . X X . . . . %e A357516 X X X . X X X X X X %Y A357516 Cf. A331986, A357234. %K A357516 nonn,walk,hard,more %O A357516 1,2 %A A357516 _Yi Yang_, Oct 01 2022 %E A357516 a(14)-a(16) from _Andrew Howroyd_, Feb 28 2023