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 A034010 #20 Jan 06 2019 06:08:03 %S A034010 0,1,2,6,20,74,300,1302,5944,28266,139010,703102,3641956,19255106, %T A034010 103630920,566522778,3140130354,17620845976,99977635264,572935630884, %U A034010 3313078283974 %N A034010 Number of 2n-step self avoiding closed walks on square grid, restricted to a quadrant and passing through origin. %H A034010 B. Hayes, <a href="https://www.jstor.org/stable/27857052">How to avoid yourself</a>, American Scientist, Vol. 86, Number 4, Jul-August 1998. p. 314-319. %e A034010 When the number of steps is 8, one of the six closed paths is %e A034010 0___. %e A034010 | ._| %e A034010 |_| %Y A034010 A subset of the polyominoes with perimeter 2n (A006725), also a subset of A002931. Cf. A000105, A038373. %K A034010 nonn,hard,walk %O A034010 1,3 %A A034010 _Felice Russo_ %E A034010 Corrected and extended by _David W. Wilson_ %E A034010 a(16)-a(18) from _Alex Chernov_, Jan 22 2012 %E A034010 a(19)-a(21) from _Bert Dobbelaere_, Jan 06 2019