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 A242279 #21 May 06 2018 11:21:52
%S A242279 1,23,252,1666,7509,26865,79920,209096,491425,1064575,2150076,4104738,
%T A242279 7458437,13005041,21857984,35598880,56353185,87019191,131364700,
%U A242279 194364050,282314901,403316353,567402672,787201416,1078078209,1459020095,1952782300,2587048786,3394568325
%N A242279 Number of inequivalent (mod D_4) ways four checkers can be placed on an n X n board.
%H A242279 Heinrich Ludwig, <a href="/A242279/b242279.txt">Table of n, a(n) for n = 2..1000</a>
%H A242279 <a href="/index/Rec#order_14">Index entries for linear recurrences with constant coefficients</a>, signature (4,-1,-16,19,20,-45,0,45,-20,-19,16,1,-4,1).
%F A242279 a(n) = (n^8 - 6*n^6 + 40*n^4 - 48*n^3 + 16*n^2 + IF(MOD(n, 2) = 1)*(14*n^4 - 48*n^3 + 34*n^2 - 3))/192.
%F A242279 G.f.: x^2*(1 + 19*x + 161*x^2 + 697*x^3 + 1446*x^4 + 2070*x^5 + 1422*x^6 + 766*x^7 + 105*x^8 + 31*x^9 + x^10 + x^11) / ((1-x)^9 * (1+x)^5). - _Vaclav Kotesovec_, May 10 2014
%F A242279 a(n) = A054772(n, 4), n >= 2. - _Wolfdieter Lang_, Oct 03 2016
%t A242279 CoefficientList[Series[x^2*(1 + 19*x + 161*x^2 + 697*x^3 + 1446*x^4 + 2070*x^5 + 1422*x^6 + 766*x^7 + 105*x^8 + 31*x^9 + x^10 + x^11) / ((1-x)^9 * (1+x)^5), {x, 0, 20}], x] (* _Vaclav Kotesovec_, May 10 2014 *)
%t A242279 LinearRecurrence[{4,-1,-16,19,20,-45,0,45,-20,-19,16,1,-4,1},{0,0,1,23,252,1666,7509,26865,79920,209096,491425,1064575,2150076,4104738},40] (* _Harvey P. Dale_, May 06 2018 *)
%Y A242279 Cf. A054252, A008805, A014409, A082966, A242358, A019318, A054772.
%K A242279 nonn,easy
%O A242279 2,2
%A A242279 _Heinrich Ludwig_, May 10 2014