This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A143902 #4 Jul 22 2025 06:11:13 %S A143902 0,1,1,1,2,1,2,3,3,2,2,4,4,4,2,3,5,6,6,5,3,3,6,7,8,7,6,3,4,7,9,10,10, %T A143902 9,7,4,4,8,10,12,12,12,10,8,4,5,9,12,14,15,15,14,12,9,5,5,10,13,16,17, %U A143902 18,17,16,13,10,5,6,11,15,18,20,21,21,20,18,15,11,6,6,12,16,20,22 %N A143902 Rectangular array R by antidiagonals: R(m,n) = number of black squares. %C A143902 Antidiagonal sums: (2,4,10,16,28,40,60,80,...)=A006584 (conjectured). %C A143902 Diagonals: A007590, A000217. %F A143902 R(m,n)=Floor(mn/2). %e A143902 Northwest corner: %e A143902 0 1 1 2 2 3 3 4 %e A143902 1 2 3 4 5 6 7 8 %e A143902 1 3 4 6 7 9 10 12 %e A143902 2 4 6 8 10 12 14 16 %Y A143902 Cf. A143901. %K A143902 nonn,tabl %O A143902 1,5 %A A143902 _Clark Kimberling_, Sep 04 2008