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 A357141 #4 Sep 15 2022 07:59:52 %S A357141 1,1,6,71,1433,44443,1968580,118159971,9240555677,913352224942, %T A357141 111374887418013,16428282185046946,2883740893056526715, %U A357141 594152447495864629867,142006380268368661423424,38973735372090120549251580,12174162204364698538764222978,4294569227671480526607187583713 %N A357141 Number of n X n triangular matrices with nonnegative integer entries and without zero rows or columns such that sum of all entries is equal to 2n. %F A357141 a(n) = A137251(2n,n). %Y A357141 Cf. A137251. %K A357141 nonn %O A357141 0,3 %A A357141 _Alois P. Heinz_, Sep 14 2022