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 A331647 #4 Jan 24 2020 07:54:12 %S A331647 1,13,313,11655,439779,14699033,453027131,14035890205,418049781331, %T A331647 11878976385087,326859368114097,8708114475309677,224507928640721933, %U A331647 5621130329235752857,136998397230581620801,3253556714665728184671,75415948071516657175683,1708706073099458659898237 %N A331647 Number of nonnegative integer matrices with 3 columns and any number of distinct nonzero rows with column sums n. %e A331647 The a(1) = 13 matrices are: %e A331647 [1 0 0] [1 0 0] [0 1 0] [0 1 0] [0 0 1] [0 0 1] %e A331647 [0 1 0] [0 0 1] [1 0 0] [0 0 1] [1 0 0] [0 1 0] %e A331647 [0 0 1] [0 1 0] [0 0 1] [1 0 0] [0 1 0] [1 0 0] %e A331647 . %e A331647 [1 1 0] [1 0 1] [1 0 0] [0 1 1] [0 1 0] [0 0 1] [1 1 1] %e A331647 [0 0 1] [0 1 0] [0 1 1] [1 0 0] [1 0 1] [1 1 0] %Y A331647 Column k=3 of A331568. %Y A331647 Cf. A331646. %K A331647 nonn %O A331647 0,2 %A A331647 _Andrew Howroyd_, Jan 23 2020