cp's OEIS Frontend

A143974 Rectangular array R by antidiagonals: label each unit square in the first quadrant lattice by its northeast vertex (x,y) and mark those having x+y=1(mod 3); then R(m,n) is the number of marked unit squares in the rectangle [0,m]x[0,n].

%I A143974 #4 Mar 30 2012 18:57:10
%S A143974 0,0,0,1,1,1,1,2,2,1,1,2,3,2,1,2,3,4,4,3,2,2,4,5,5,5,4,2,2,4,6,6,6,6,
%T A143974 4,2,3,5,7,8,8,8,7,5,3,3,6,8,9,10,10,9,8,6,3,3,6,9,10,11,12,11,10,9,6,
%U A143974 3,4,7,10,12,13,14,14,13,12,10,7,4,4,8,11,13,15,16,16,16,15,13,11,8,4,4,8
%N A143974 Rectangular array R by antidiagonals: label each unit square in the first quadrant lattice by its northeast vertex (x,y) and mark those having x+y=1(mod 3); then R(m,n) is the number of marked unit squares in the rectangle [0,m]x[0,n].
%C A143974 Diagonals: A000212, A128422, A032765, A143975, A071408.
%C A143974 Rows: A002264, A004523, A000027, A004773, A138235, A005843, A047349 et al.
%F A143974 R(m,n)=floor(mn/3).
%e A143974 Northwest corner:
%e A143974 0 0 1 1 1 2
%e A143974 0 1 2 2 3 4
%e A143974 1 2 3 4 5 6
%e A143974 1 2 4 5 6 8
%e A143974 1 3 5 6 8 10
%e A143974 R(3,4) counts these marked squares: (1,3), (2,2), (3,1), (3,4).
%Y A143974 Cf. A143976, A143977.
%K A143974 nonn,tabl
%O A143974 1,8
%A A143974 _Clark Kimberling_, Sep 06 2008