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