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 A331197 #11 Jan 24 2020 15:54:39 %S A331197 0,1,7,28,104,332,1032,2983,8384,22622,59479,151902,379616,927521, %T A331197 2224100,5236410,12130549,27669296,62229605,138095206,302672402, %U A331197 655627183,1404598865,2977830134,6251059210,12999297747,26791987616,54750232180,110977385294,223204454700,445590973235 %N A331197 Number of nonnegative integer matrices with 2 distinct columns and any number of nonzero rows with each column sum being n and rows in nonincreasing lexicographic order. %C A331197 The condition that the rows be in nonincreasing order is equivalent to considering nonequivalent matrices up to permutation of rows. %H A331197 Andrew Howroyd, <a href="/A331197/b331197.txt">Table of n, a(n) for n = 0..400</a> %F A331197 a(n) = A002774(n) - A000041(n). %e A331197 The a(2) = 7 matrices are: %e A331197 [2 1] [2 0] [1 2] [1 1] [2 0] [1 0] [1 0] %e A331197 [0 1] [0 2] [1 0] [1 0] [0 1] [1 0] [1 0] %e A331197 [0 1] [0 1] [0 2] [0 1] %e A331197 [0 1] %e A331197 See the example in A331197 for the a(3) = 28 case. %Y A331197 Column k=2 of A331161. %Y A331197 Cf. A000041, A002774, A331197. %K A331197 nonn %O A331197 0,3 %A A331197 _Andrew Howroyd_, Jan 11 2020