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 A331706 #5 Jan 25 2020 20:55:05 %S A331706 0,1,6,42,268,1239,7278,40828,201084,1044693,5171998,24532674, %T A331706 116470596,546141979,2505755010,11318525016,50046272884,219637249269, %U A331706 944072863998,4029243437158,16977344149608,70370874102975,289702060529770,1177283903977008,4740700176809748 %N A331706 Number of nonnegative integer matrices with 2 distinct columns and any number of distinct nonzero rows with column sums n and columns in decreasing lexicographic order. %C A331706 The condition that the columns be in decreasing order is equivalent to considering nonequivalent matrices with distinct columns up to permutation of columns. %F A331706 a(n) = (A331646(n) - A032020(n)) / 2. %e A331706 The a(2) = 6 matrices are: %e A331706 [1 1] [1 0] [1 0] [2 1] [2 0] [1 0] %e A331706 [1 0] [1 1] [0 1] [0 1] [0 2] [1 2] %e A331706 [0 1] [0 1] [1 1] %Y A331706 Column k=2 of A331570. %Y A331706 Cf. A032020, A331646, A331707. %K A331706 nonn %O A331706 0,3 %A A331706 _Andrew Howroyd_, Jan 25 2020