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 A172138 #24 Mar 11 2023 09:20:53
%S A172138 0,4,84,452,1772,5596,14888,34640,72712,140716,255036,437968,718980,
%T A172138 1136092,1737376,2582576,3744848,5312620,7391572,10106736,13604716,
%U A172138 18056028,23657560,30635152,39246296,49782956,62574508,77990800
%N A172138 Number of ways to place 3 nonattacking zebras on an n X n board.
%C A172138 A zebra is a (fairy chess) leaper [2,3].
%H A172138 Vincenzo Librandi, <a href="/A172138/b172138.txt">Table of n, a(n) for n = 1..1000</a>
%H A172138 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 A172138 <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (7,-21,35,-35,21,-7,1).
%F A172138 a(n) = (n^6 - 27*n^4 + 120*n^3 + 74*n^2 - 1608*n + 2976)/6, n >=6.
%F A172138 G.f.: 4*x^2*(1 + 14*x - 13*x^2 + 58*x^3 - 29*x^4 - 9*x^5 + x^6 + 33*x^7 - 45*x^8 + 23*x^9 - 4*x^10)/(1-x)^7. - _Vaclav Kotesovec_, Mar 25 2010
%t A172138 CoefficientList[Series[4x(1+14*x-13*x^2+58*x^3-29*x^4-9*x^5+x^6+ 33*x^7- 45*x^8 +23*x^9-4*x^10)/(1-x)^7, {x, 0, 40}], x] (* _Vincenzo Librandi_, May 27 2013 *)
%t A172138 LinearRecurrence[{7,-21,35,-35,21,-7,1},{0,4,84,452,1772,5596,14888,34640,72712,140716,255036,437968},30] (* _Harvey P. Dale_, Mar 11 2023 *)
%o A172138 (Magma) [0,4,84,452,1772] cat [(n^6 -27*n^4 +120*n^3 +74*n^2 -1608*n +2976)/6: n in [6..50]]; // _G. C. Greubel_, Apr 19 2022
%o A172138 (SageMath) [0,4,84,452,1772]+[(n^6 -27*n^4 +120*n^3 +74*n^2 -1608*n +2976)/6 for n in (6..50)] # _G. C. Greubel_, Apr 19 2022
%Y A172138 Cf. A047659, A172124, A172134, A172137.
%K A172138 nonn,easy
%O A172138 1,2
%A A172138 _Vaclav Kotesovec_, Jan 26 2010