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 A202654 #16 Aug 23 2024 12:20:33
%S A202654 0,0,3,52,370,1620,5285,14168,33012,69240,133815,242220,415558,681772,
%T A202654 1076985,1646960,2448680,3552048,5041707,7018980,9603930,12937540,
%U A202654 17184013,22533192,29203100,37442600,47534175,59796828,74589102,92312220,113413345,138388960
%N A202654 Number of ways to place 3 nonattacking semi-queens on an n X n board.
%C A202654 Two semi-queens do not attack each other if they are in the same northwest-southeast diagonal.
%H A202654 Michael De Vlieger, <a href="/A202654/b202654.txt">Table of n, a(n) for n = 1..10000</a>
%H A202654 Christopher R. H. Hanusa, Thomas Zaslavsky, <a href="https://arxiv.org/abs/1906.08981">A q-queens problem. VII. Combinatorial types of nonattacking chess riders</a>, arXiv:1906.08981 [math.CO], 2019.
%H A202654 V. Kotesovec, <a href="https://oeis.org/wiki/User:Vaclav_Kotesovec">Non-attacking chess pieces</a>
%H A202654 <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (7, -21, 35, -35, 21, -7, 1).
%F A202654 a(n) = 1/6*(n-2)*(n-1)*n*(n^3-5*n^2+8*n-3).
%F A202654 G.f.: -x^3*(17*x^3 + 69*x^2 + 31*x + 3)/(x-1)^7.
%t A202654 Rest@ CoefficientList[Series[-x^3*(17 x^3 + 69 x^2 + 31 x + 3)/(x - 1)^7, {x, 0, 32}], x] (* _Michael De Vlieger_, Aug 19 2019 *)
%Y A202654 Cf. A099152, A047659, A103220, A202655, A202656, A202657.
%K A202654 nonn
%O A202654 1,3
%A A202654 _Vaclav Kotesovec_, Dec 22 2011