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 A006494 #48 Feb 16 2025 08:32:30 %S A006494 1,20,400,8902,197281,4865617,119060679,3195913043,84999425906, %T A006494 2439540533153,69353270203366,2097660204806910,62855340727822758, %U A006494 1981075507583376209 %N A006494 Number of possible chess games at the end of the n-th ply plus number of games that terminate (i.e., mate) in fewer than n plies. %C A006494 This sequence is A048987 plus the cumulative sum of A079485. - _Richard Bean_, Jun 18 2003 %C A006494 The word "terminate" is inappropriate if only termination by checkmate is considered, since games can also end in a draw. The earliest possible draws occur by threefold or 5-fold repetition of the starting position through, e.g., twofold resp. 4-fold repetition of the moves 1.Nf3 Nf6 2.Ng1 Ng8, or an equivalent sequence. - _M. F. Hasler_, Mar 02 2022 %D A006494 James Gleick, Faster, Vintage Books, NY, 2000 (see pp. 259-261). %H A006494 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Chess.html">Chess</a> %H A006494 <a href="/index/Ch#chess">Index entries for sequences related to number of chess games</a> %Y A006494 Cf. A048987, A079485. %K A006494 nonn,hard,nice,fini,more %O A006494 0,2 %A A006494 Ken Thompson (ken(AT)google.com) %E A006494 a(8)-a(10) from _François Labelle_, Jan 22 2004 %E A006494 a(11) from _François Labelle_, Jul 25 2004, who thanks Joost de Heer for providing computer time %E A006494 a(12) from _François Labelle_, Mar 04 2012 %E A006494 a(13) from _François Labelle_, Aug 15 2017