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 A190399 #14 Sep 12 2015 11:00:26
%S A190399 0,1,54,1068,8550,45873,177968,562032,1519560,3662625,8057390,
%T A190399 16477020,31712850,58018793,101639700,171525568,280160068,444636297,
%U A190399 687881890,1040201500,1541008350,2240952065,3204279960,4511682288
%N A190399 Number of ways to place 4 nonattacking grasshoppers on a toroidal chessboard of size n x n.
%C A190399 The Grasshopper moves on the same lines as a queen, but must jump over a hurdle to land on the square immediately beyond.
%H A190399 Vincenzo Librandi, <a href="/A190399/b190399.txt">Table of n, a(n) for n = 1..1000</a>
%H A190399 V. Kotesovec, <a href="https://oeis.org/wiki/User:Vaclav_Kotesovec">Number of ways of placing non-attacking queens, kings, bishops and knights</a> (in English and Czech)
%F A190399 a(n) = 1/24*n^2*(n^6 -6*n^4 -96*n^3 +347*n^2 +96*n -726 +96*(-1)^n), n>4.
%F A190399 G.f.: -x^2*(80*x^14 -444*x^13 +768*x^12 +108*x^11 -1824*x^10 +1600*x^9 +1025*x^8 -1200*x^7 +708*x^6 +1772*x^5 +7254*x^4 +2788*x^3 +756*x^2 +48*x +1)/((x-1)^9*(x+1)^3).
%t A190399 CoefficientList[Series[- x (80 x^14 - 444 x^13 + 768 x^12 + 108 x^11 - 1824 x^10 + 1600 x^9 + 1025 x^8 - 1200 x^7 + 708 x^6 + 1772 x^5 + 7254 x^4 + 2788 x^3 + 756 x^2 + 48 x + 1) / ((x - 1)^9 (x + 1)^3), {x, 0, 50}], x] (* _Vincenzo Librandi_, Jun 03 2013 *)
%Y A190399 Cf. A190396, A190398, A172519.
%K A190399 nonn,easy
%O A190399 1,3
%A A190399 _Vaclav Kotesovec_, May 10 2011