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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: (1,4), (2,2), (3,3), (4,1); then R(m,n) is the number of UNmarked squares in the rectangle [0,m]x[0,n].
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%I #7 Dec 06 2017 10:56:19

%S 1,2,2,3,3,3,3,5,5,3,4,6,7,6,4,5,8,9,9,8,5,6,9,12,12,12,9,6,6,11,14,

%T 15,15,14,11,6,7,12,16,18,19,18,16,12,7,8,14,18,21,23,23,21,18,14,8,9,

%U 15,21,24,27,27,27,24,21,15,9,9,17,23,27,30,32,32,30,27,23,17,9,10,18,25

%N 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: (1,4), (2,2), (3,3), (4,1); then R(m,n) is the number of UNmarked squares in the rectangle [0,m]x[0,n].

%C Row 4n is given by n*(1,2,3,4,5,6,...).

%H G. C. Greubel, <a href="/A143997/b143997.txt">Table of n, a(n) for the first 50 rows, flattened</a>

%F R(m,n) = m*n - floor(m*n/4).

%t b[n_, m_] := m*n - Floor[m*n/4]; a:= Table[a[n, m], {n, 1, 25}, {m, 1, 25}]; Table[b[[k, n - k + 1]], {n, 1, 20}, {k, 1, n}] // Flatten (* _G. C. Greubel_, Dec 05 2017 *)

%Y Cf. A143996, A143998, A143999, A144000, A144001.

%K nonn,tabl

%O 1,2

%A _Clark Kimberling_, Sep 07 2008