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 A172141 #18 Apr 23 2022 18:37:23
%S A172141 0,6,28,96,240,518,980,1712,2784,4310,6380,9136,12688,17206,22820,
%T A172141 29728,38080,48102,59964,73920,90160,108966,130548,155216,183200,
%U A172141 214838,250380,290192,334544,383830,438340,498496,564608,637126
%N A172141 Number of ways to place 2 nonattacking nightriders on an n X n board.
%C A172141 A nightrider is a fairy chess piece that can move (proportionate to how a knight moves) in any direction.
%D A172141 Christian Poisson, Echecs et mathematiques, Rex Multiplex 29/1990, p.829
%H A172141 Vincenzo Librandi, <a href="/A172141/b172141.txt">Table of n, a(n) for n = 1..1000</a>
%H A172141 Christopher R. H. Hanusa, T. Zaslavsky, and S. Chaiken, <a href="http://arxiv.org/abs/1609.00853">A q-Queens Problem. IV. Queens, Bishops, Nightriders (and Rooks)</a>, arXiv preprint arXiv:1609.00853, a12016
%H A172141 Vaclav Kotesovec, <a href="https://oeis.org/wiki/User:Vaclav_Kotesovec">Number of ways of placing non-attacking queens and kings on boards of various sizes</a>
%H A172141 <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (3,-1,-5,5,1,-3,1).
%F A172141 Explicit formula (Christian Poisson, 1990): a(n) = n*(3*n^3 - 5*n^2 + 9*n - 4)/6 if n is even and a(n) = n*(n - 1)*(3*n^2 - 2*n + 7)/6 if n is odd.
%F A172141 G.f.: 2*x^2*(3+2*x+x^2)*(1+x+2*x^2)/((1-x)^5*(1+x)^2). - _Vaclav Kotesovec_, Mar 25 2010
%F A172141 From _G. C. Greubel_, Apr 21 2022: (Start)
%F A172141 a(n) = (1/12)*n*(3*(-1)^n - (11 - 18*n + 10*n^2 - 6*n^3)).
%F A172141 E.g.f.: (x/12)*(-3*exp(-x) + (3 + 30*x + 26*x^2 + 6*x^3)exp(x)). (End)
%t A172141 CoefficientList[Series[2*x*(3+2*x+x^2)*(1+x+2*x^2)/((1-x)^5*(1+x)^2), {x,0,40}], x] (* _Vincenzo Librandi_, May 27 2013 *)
%o A172141 (Magma) [(n/12)*(3*(-1)^n -(11 -18*n +10*n^2 -6*n^3)): n in [1..40]]; // _G. C. Greubel_, Apr 21 2022
%o A172141 (SageMath) [(n/12)*(3*(-1)^n -(11 -18*n +10*n^2 -6*n^3)) for n in (1..40)] # _G. C. Greubel_, Apr 21 2022
%Y A172141 Cf. A036464, A172123, A172132, A172137.
%K A172141 easy,nonn
%O A172141 1,2
%A A172141 _Vaclav Kotesovec_, Jan 26 2010