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