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 A331649 #7 Jan 25 2020 02:28:32 %S A331649 1,0,3,17,230,3264,60338,1287062,31900620,893284155,27972470286, %T A331649 967596779631,36654913572018,1509052435744560,67089897326522970, %U A331649 3203343744126663616,163486870943294124046,8881542959996746368420,511713241494851800728865,31165957861936237845310435 %N A331649 Number of binary matrices with n distinct columns and any number of distinct nonzero rows with 2 ones in every column and columns in decreasing lexicographic order. %C A331649 The condition that the columns be in decreasing order is equivalent to considering nonequivalent matrices with distinct columns up to permutation of columns. %H A331649 Andrew Howroyd, <a href="/A331649/b331649.txt">Table of n, a(n) for n = 0..200</a> %e A331649 The a(2) = 3 matrices are: %e A331649 [1 1] [1 0] [1 0] %e A331649 [1 0] [1 1] [0 1] %e A331649 [0 1] [0 1] [1 1] %Y A331649 Row n=2 of A331569. %K A331649 nonn %O A331649 0,3 %A A331649 _Andrew Howroyd_, Jan 24 2020