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 A121789 #12 Jan 10 2019 22:39:39
%S A121789 2,8,34,650,12014,1016492,83761994,32647369000,12227920752840,
%T A121789 22181389298814376,38166266554504010420,323646210116765453608746,
%U A121789 2574827340090912815899810042,102299512403818451392332665527950
%N A121789 "Spanning Hamiltonian walks" on the square lattice (see Jensen web site for further information).
%C A121789 Number of Hamiltonian paths in the graph P_{n+1} X P_{n+1} starting at any of the n+1 vertices on one side of the graph and terminating at any of the n+1 vertices on the opposite side. - _Andrew Howroyd_, Apr 10 2016
%H A121789 I. Jensen, <a href="/A121789/b121789.txt">Table of n, a(n) for n = 1..18</a> [from the Jensen link below]
%H A121789 I. Jensen, <a href="https://web.archive.org/web/20070612141707/http://www.ms.unimelb.edu.au/~iwan/saw/SAW_ser.html">Series Expansions for Self-Avoiding Walks</a>
%H A121789 I. Jensen, <a href="https://web.archive.org/web/20070613021722/http://www.ms.unimelb.edu.au/~iwan/saw/series/hami_span.ser">Spanning Hamiltonian walks</a>
%Y A121789 Cf. A120443, A121785, A215527.
%K A121789 nonn
%O A121789 1,1
%A A121789 _N. J. A. Sloane_, Aug 30 2006