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A143998 Rectangular array by antidiagonals: label each unit square in the first quadrant lattice by its northeast vertex (x,y) and mark squares for which (x,y) is congruent mod 4 to one of the following: (1,1), (2,3), (3,2), (4,0); then R(m,n) is the number of marked squares in the rectangle [0,m]x[0,n].

%I A143998 #7 Dec 06 2017 10:56:26
%S A143998 0,1,1,2,3,2,3,4,4,3,3,6,6,6,3,4,7,9,9,7,4,5,9,11,12,11,9,5,6,10,13,
%T A143998 15,15,13,10,6,6,12,15,18,18,18,15,12,6,7,13,18,21,22,22,21,18,13,7,8,
%U A143998 15,20,24,26,27,26,24,20,15,8,9,16,22,27,30,31,31,30,27,22,16,9,9,18,24,30
%N A143998 Rectangular array by antidiagonals: label each unit square in the first quadrant lattice by its northeast vertex (x,y) and mark squares for which (x,y) is congruent mod 4 to one of the following: (1,1), (2,3), (3,2), (4,0); then R(m,n) is the number of marked squares in the rectangle [0,m]x[0,n].
%C A143998 Row 4n is given by 3n*(1,2,3,4,5,6,...).
%H A143998 G. C. Greubel, <a href="/A143998/b143998.txt">Table of n, a(n) for the first 50 rows, flattened</a>
%F A143998 R(m,n) = floor(3*m*n/4).
%t A143998 b[n_, m_] := Floor[3*m*n/4]; a:= Table[a[n, m], {n, 1, 25}, {m, 1, 25}]; Table[a[[k, n - k + 1]], {n, 1, 20}, {k, 1, n}]//Flatten (* _G. C. Greubel_, Dec 05 2017 *)
%Y A143998 Cf. A143996, A143997, A143999, A144000, A144001.
%K A143998 nonn,tabl
%O A143998 1,4
%A A143998 _Clark Kimberling_, Sep 07 2008