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 A331711 #6 Jan 25 2020 20:55:43 %S A331711 1,2,7,45,271,1244,7289,40841,201103,1044720,5172055,24532739, %T A331711 116470697,546142112,2505755203,11318525367,50046273319,219637249886, %U A331711 944072864849,4029243438335,16977344151163,70370874105726,289702060533067,1177283903981765,4740700176816041 %N A331711 Number of nonnegative integer matrices with 2 columns and any number of distinct nonzero rows with column sums n and columns in nonincreasing lexicographic order. %C A331711 The condition that the columns be in nonincreasing order is equivalent to considering nonequivalent matrices up to permutation of columns. %F A331711 a(n) = (A331646(n) + A032020(n)) / 2. %e A331711 The a(2) = 2 matrices are: %e A331711 [1 1] [1 0] [1 0] [2 1] [2 0] [1 0] [2 2] %e A331711 [1 0] [1 1] [0 1] [0 1] [0 2] [1 2] %e A331711 [0 1] [0 1] [1 1] %Y A331711 Column k=2 of A331572. %Y A331711 Cf. A032020, A331646, A331712. %K A331711 nonn %O A331711 0,2 %A A331711 _Andrew Howroyd_, Jan 25 2020