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 A098500 #9 Jun 17 2017 02:52:17 %S A098500 1,3,12,32,59,91,130,176,229,289,356,430,511,599,694,796,905,1021, %T A098500 1144,1274,1411,1555,1706,1864,2029,2201,2380,2566,2759,2959,3166, %U A098500 3380,3601,3829,4064,4306,4555,4811,5074,5344,5621,5905,6196,6494,6799,7111,7430 %N A098500 Number of squares on infinite quarter chessboard at <=n knight moves from the corner. %H A098500 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1). %F A098500 a(n) = (1/2) * (7*n^2 + n + 2), for n>3. %F A098500 G.f.: -(2*x^6-2*x^5-4*x^4+4*x^3+6*x^2+1) / (x-1)^3. - _Colin Barker_, Jul 15 2013 %e A098500 3 squares are reachable after 1 move, from these you can reach 8 new squares more, so a(1)=3, a(2)=12. %Y A098500 First differences are in A047883. %Y A098500 See A018836 (unbounded), A098498 (halfplane), A098499 (diagonal halfplane), A098501 (octant). %K A098500 nonn,easy %O A098500 0,2 %A A098500 _Ralf Stephan_, Sep 15 2004 %E A098500 More terms from _Colin Barker_, Jul 15 2013