Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #11 Sep 12 2019 09:40:39
%S 0,1,6,104,4736,770112,440994608,896679244544,6513978322585408,
%T 170630215971902124288,16261454692523251085611648,
%U 5683372715412699486531047331840,7334542846356464931239079919515090432,35157828307617499760690834338506768579289088
%N Number of unlabeled digraphs with n nodes and an odd number of arcs.
%H Andrew Howroyd, <a href="/A055969/b055969.txt">Table of n, a(n) for n = 1..50</a>
%F a(n) = (A000273(n)-A003086(n))/2.
%t A000273 = Cases[Import["https://oeis.org/A000273/b000273.txt", "Table"], {_, _}][[All, 2]];
%t A003086 = Cases[Import["https://oeis.org/A003086/b003086.txt", "Table"], {_, _}][[All, 2]];
%t a[n_] := (A000273[[n + 1]] - A003086[[n]])/2;
%t Array[a, 50] (* _Jean-François Alcover_, Sep 12 2019, after _Andrew Howroyd_ *)
%Y Cf. A054928, A007869, A054960.
%K easy,nonn
%O 1,3
%A _Vladeta Jovovic_, Jul 19 2000
%E Terms a(14) and beyond from _Andrew Howroyd_, Sep 17 2018