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 A320808 #10 Jul 09 2025 04:48:17 %S A320808 1,0,0,1,0,0,1,0,1,2,0,0,1,0,1,2,0,1,2,3,0,0,1,0,2,4,0,1,5,4,0,1,5,5, %T A320808 5,0,0,1,0,2,4,0,2,10,8,0,1,9,13,7,0,1,5,12,9,7,0,0,1,0,3,6,0,3,16,12, %U A320808 0,2,24,33,16,0,1,14,36,29,12,0,1,9,23,29 %N A320808 Regular tetrangle where T(n,k,i) is the number of nonnegative integer matrices up to row and column permutations with no zero rows or columns and k nonzero entries summing to n, with i columns. %e A320808 Tetrangle begins: %e A320808 1 0 0 0 0 0 %e A320808 0 1 0 1 0 1 0 1 0 1 %e A320808 0 1 2 0 1 2 0 2 4 0 2 4 %e A320808 0 1 2 3 0 1 5 4 0 2 10 8 %e A320808 0 1 5 5 5 0 1 9 13 7 %e A320808 0 1 5 12 9 7 %Y A320808 Triangle sums are A007716. Triangle of row sums is A320801. Triangle of column sums is A317533. Triangle of last columns (without its leading column 1,0,0,0,...) is A055884. %Y A320808 Cf. A000219, A008284, A316980, A316983, A318805, A319616, A320796, A321194. %K A320808 nonn,tabf %O A320808 1,10 %A A320808 _Gus Wiseman_, Nov 09 2018