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 A054547 #16 Jan 29 2022 12:16:03
%S A054547 0,0,2,1,0,0,12,20,15,6,1,0,0,12,140,435,768,920,792,495,220,66,12,1,
%T A054547 0,0,0,240,2520,11604,34150,73560,123495,166860,184426,167900,125965,
%U A054547 77520,38760,15504,4845,1140,190,20,1
%N A054547 Triangular array giving number of labeled digraphs on n unisolated nodes and k=0..n*(n-1) arcs.
%H A054547 Andrew Howroyd, <a href="/A054547/b054547.txt">Table of n, a(n) for n = 1..2680</a> (rows 1..20)
%F A054547 T(n, k) = Sum_{i=0..n} (-1)^(n-i)*binomial(n, i)*binomial(i*(i-1), k).
%e A054547 Triangle T(n,k) begins:
%e A054547 [0],
%e A054547 [0,2,1],
%e A054547 [0,0,12,20,15,6,1],
%e A054547 [0,0,12,140,435,768,920,792,495,220,66,12,1],
%e A054547 ...
%o A054547 (PARI) row(n) = {Vecrev(sum(i=0, n, (-1)^(n-i)*binomial(n,i)*(1 + 'y)^(i*(i-1))), n*(n-1)+1)}
%o A054547 { for(n=1, 6, print(row(n))) } \\ _Andrew Howroyd_, Jan 28 2022
%Y A054547 Row sums are A054545.
%Y A054547 Column sums are A121252.
%Y A054547 The unlabeled version is A350908.
%Y A054547 Cf. A054548 (graphs), A062735, A123554.
%K A054547 easy,nonn,tabf
%O A054547 1,3
%A A054547 _Vladeta Jovovic_, Apr 09 2000