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 A098499 #8 Jun 17 2017 04:00:45 %S A098499 1,5,23,57,109,169,246,334,439,555,688,832,993,1165,1354,1554,1771, %T A098499 1999,2244,2500,2773,3057,3358,3670,3999,4339,4696,5064,5449,5845, %U A098499 6258,6682,7123,7575,8044,8524,9021,9529,10054,10590,11143,11707,12288,12880,13489 %N A098499 Number of squares on infinite half chessboard at <=n knight moves from a fixed point on the diagonal. %H A098499 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,0,-2,1). %F A098499 a(n) = (1/4) [28n^2 - 6n + 9 + 3(-1)^n], for n>3. %F A098499 G.f.: -(3*x^7-x^6-8*x^5+4*x^4+13*x^3+13*x^2+3*x+1) / ((x-1)^3*(x+1)). - _Colin Barker_, Jul 14 2013 %e A098499 5 squares are reachable after 1 move, from these you can reach 18 new squares more, so a(1)=5, a(2)=23. %Y A098499 Equals A098498(n) - A052938(n-4), n>3. %Y A098499 See A018836 (unbounded), A098498 (halfplane), A098500 (quadrant), A098501 (octant). %K A098499 nonn,easy %O A098499 0,2 %A A098499 _Ralf Stephan_, Sep 15 2004 %E A098499 More terms from _Colin Barker_, Jul 14 2013