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 A057278 #12 Jan 22 2022 23:42:30
%S A057278 1,0,1,1,0,0,1,4,4,1,1,0,0,0,1,11,31,45,38,27,13,5,1,1,0,0,0,0,1,23,
%T A057278 152,486,992,1419,1641,1485,1152,707,379,154,61,16,5,1,1,0,0,0,0,0,1,
%U A057278 42,517,3194,12174,32860,68423,116168,166164,204867,219906,206993,170922,124088,78809,43860,21209,8951,3242,1043,288,76,17,5,1,1
%N A057278 Triangle T(n,k) of number of digraphs with a source and a sink on n unlabeled nodes and k arcs, k=0..n*(n-1).
%D A057278 V. Jovovic, G. Kilibarda, Enumeration of labeled initially-finally connected digraphs, Scientific review, Serbian Scientific Society, 19-20 (1996), p. 246.
%H A057278 Andrew Howroyd, <a href="/A057278/b057278.txt">Table of n, a(n) for n = 1..2680</a> (rows 1..20)
%e A057278 Triangle begins:
%e A057278 [1],
%e A057278 [0,1,1],
%e A057278 [0,0,1,4,4,1,1],
%e A057278 [0,0,0,1,11,31,45,38,27,13,5,1,1],
%e A057278 ...
%e A057278 The number of digraphs with a source and a sink on 3 unlabeled nodes is 11 = 1+4+4+1+1.
%o A057278 (PARI) \\ See PARI link in A350794 for program code.
%o A057278 { my(A=A057278triang(5)); for(n=1, #A, print(A[n])) } \\ _Andrew Howroyd_, Jan 21 2022
%Y A057278 Row sums give A049531.
%Y A057278 Column sums give A350906.
%Y A057278 The labeled version is A057271.
%Y A057278 Cf. A057270, A057276, A057277, A057279, A350794, A350795.
%K A057278 nonn,tabf
%O A057278 1,8
%A A057278 _Vladeta Jovovic_, Goran Kilibarda, Sep 14 2000
%E A057278 Terms a(46) and beyond from _Andrew Howroyd_, Jan 21 2022