A054933 Number of unlabeled digraphs on n nodes up to reversing the arcs.

1, 3, 13, 144, 5158, 778084, 441288796, 896699384640, 6513980949408584, 170630216624502796000, 16261454692830032538976880, 5683372715412978313604073582912, 7334542846356465411966209047539403296, 35157828307617499762304829312302735958971072, 629172630775224433640531447950565255471723325434560

Offset: 1

Author

N. J. A. Sloane, May 24 2000

Keywords

• nonn
• easy

Links

• Andrew Howroyd, Table of n, a(n) for n = 1..50
• A. Gainer-Dewar, Pólya theory for species with an equivariant group action, arXiv:1401.6202 [math.CO], 2014. Also Andrew Gainer-Dewar, Species with an equivariant group action, AUSTRALASIAN JOURNAL OF COMBINATORICS, Volume 63(2) (2015), Pages 202-225.
• V. A. Liskovets, Some easily derivable sequences, J. Integer Sequences, 3 (2000), #00.2.2.

Crossrefs

Cf. A000273, A002499.

Programs

Mathematica

A000273 = Cases[Import["https://oeis.org/A000273/b000273.txt", "Table"], {, }][[All, 2]];
A002499 = Cases[Import["https://oeis.org/A002499/b002499.txt", "Table"], {, }][[All, 2]];
a[n_] := (A000273[[n + 1]] + A002499[[n]])/2;
Array[a, 50] (* Jean-François Alcover, Aug 29 2019 *)

Formula

a(n) = (A000273(n) + A002499(n))/2.