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 A121252 #8 Nov 20 2023 04:24:42
%S A121252 1,2,25,520,15150,567540,25986334,1406214816,87803248260,
%T A121252 6213408758960,491423381371208,42958461746823376,4112928296979824348,
%U A121252 428022362222941505760,48106759414197240877200,5807382441785322296139392
%N A121252 Number of labeled digraphs without isolated vertices and with n arcs.
%F A121252 a(n) = Sum_{m>=0} binomial(m*(m-1),n)/2^(m+1). Column sums of A054547.
%p A121252 seq(value(Sum(binomial(m*(m-1),n)/2^(m+1),m=0..infinity)),n=0..20); # _Vladeta Jovovic_, Aug 25 2006
%Y A121252 Cf. A054545, A053418 (unlabeled).
%K A121252 easy,nonn
%O A121252 0,2
%A A121252 _Vladeta Jovovic_, Aug 22 2006
%E A121252 More terms from _Max Alekseyev_, Aug 23 2006