%I
%S 1,1,1,4,59,2616,306117,87716644,58874478231,90018247082416,
%T 307775459402071913,2322338398654088751036,38293189001166839643861795,
%U 1369158635491114830895696234696,105480725505896171175318367295035341
%N Number of labeled essential directed acyclic graphs (DAGs).
%H Bertran Steinsky, <a href="https://doi.org/10.1016/S0012365X(02)008385">Enumeration of labelled chain graphs and labeled essential directed acyclic graphs</a>, Discrete Mathematics, 270 (2003), 267278.
%F a(0)=1, a(n) = Sum_{k=1..n} (1)^(k+1) * binomial(n, k) * (2^(nk)n+k) * a(nk) [from Steinsky].  _Sean A. Irvine_, Oct 06 2019
%K nonn
%O 0,4
%A Detlef Pauly (dettodet(AT)yahoo.de), Aug 22 2003
%E a(0)=1 inserted by _Sean A. Irvine_, Oct 06 2019
