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 A285873 #10 Apr 17 2022 01:00:41 %S A285873 1,21,441,9872,220447,5247292,124278971,3113440755,77520962327, %T A285873 2024021927610 %N A285873 Number of possible chess games at the end of the n-th ply starting without queens. %C A285873 Gives the number of possible chess games where both sides start without queens. Queens are still allowed to appear later in the game through promotion. %C A285873 Does not include games which end in fewer than n plies. %C A285873 The total number of such games should be less than the total number of standard chess games, and it appears A285873(n) <= A048987(n) for n >= 7. %C A285873 Initial terms computed using the Chesspresso engine. %H A285873 <a href="http://www.chesspresso.org/">Chesspresso<sup>TM</sup></a>. %e A285873 a(1) = 21 because there are 20 usual opening moves plus the additional move of moving the king into the vacant square where the queen would usually be. %Y A285873 Cf. A048987 (standard), A285874 (no rooks), A285875 (no knights), A285876 (no bishops), A285877 (no pawns), A285878 (pawns and king). %K A285873 nonn,hard,more,fini %O A285873 0,2 %A A285873 _Sean A. Irvine_, Apr 28 2017