%I #5 Jul 10 2018 02:59:40
%S 1,3,57,3963,1040097
%N Number of indecomposable binary relations on [n].
%H Vincent Pilaud, Viviane Pons, <a href="https://arxiv.org/abs/1807.03277">The Hopf algebra of integer binary relations</a>, arXiv:1807.03277 [math.CO], 2018. See Table 2 p.8.
%F a(n) <= A053763(n).
%Y Cf. A053763.
%K nonn,more
%O 1,2
%A _Michel Marcus_, Jul 09 2018