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 A004147 M5233 #28 May 17 2023 14:41:24 %S A004147 32,9784,7571840,11140566368 %N A004147 Number of n-state Turing machines which halt. %C A004147 This sequence is noncomputable, because it could be used to solve the halting problem. In fact, it is of the same degree of difficulty as the halting problem. - David Diamondstone (skeptical.scientist(AT)gmail.com), Dec 28 2007 %D A004147 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %H A004147 J. P. Jones, <a href="http://www.jstor.org/stable/2319560">Recursive undecidability - an exposition</a>, Amer. Math. Monthly, 81 (1974), 724-738. %H A004147 H. Marxen, <a href="http://turbotm.de/~heiner/BB/">Busy Beaver</a> %H A004147 Michael Somos, <a href="https://grail.eecs.csuohio.edu/~somos/bb.html">Busy Beaver Turing Machine</a> %H A004147 Michael Somos, <a href="https://grail.eecs.csuohio.edu/~somos/busy.html">Busy Beaver</a> %H A004147 <a href="/index/Br#beaver">Index entries for sequences related to Busy Beaver problem</a> %Y A004147 Cf. A028444, A052200. %K A004147 nonn,nice,hard,bref %O A004147 1,1 %A A004147 _N. J. A. Sloane_ %E A004147 More terms from David Diamondstone (skeptical.scientist(AT)gmail.com), Dec 28 2007 %E A004147 a(4) from _Jonathan Lee_, who enumerated all 25.6 billion 4-state machines up to 107 steps, Mar 05 2016