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 A258486 #17 Jul 22 2015 00:23:44
%S A258486 1,1,5,151,9944,1196991,226435150,61992679960,23198439767669,
%T A258486 11380100883484302,7087878538028540725,5465174495550911165171,
%U A258486 5111311778783673593594175,5701234859347275019419890715,7477492710871626347942014991975,11393306956061559325223329489826611,19958666934810234750929365717573438949,39835206091758734935374720734513530255512,89867076346063005007676287874769844881101800,227547795689116560408812799327387232156371842150
%N A258486 Number of tangled chains of length k=3.
%C A258486 Tangled chains are ordered lists of k rooted binary trees with n leaves and a matching between each leaf from the i-th tree with a unique leaf from the (i+1)st tree up to isomorphism on the binary trees. This sequence fixes k=3, and n = 1,2,3,...
%D A258486 R. Page, Tangled trees: phylogeny, cospeciation, and coevolution, The University of Chicago Press, 2002.
%H A258486 Sara Billey, Matjaž Konvalinka, and Frederick A. Matsen IV, <a href="http://arxiv.org/abs/1507.04976">On the enumeration of tanglegrams and tangled chains</a>, (2015).
%F A258486 t(n) = Sum_{b=(b(1),...,b(t))} Product_{i=2..t} (2(b(i)+...+b(t))-1)^3)/z(b) where the sum is over all binary partitions of n and z(b) is the size of the stabilizer of a permutation of cycle type b under conjugation.
%Y A258486 Cf. A000123 (binary partitions), A258485 (tanglegrams), A258487, A258488, A258489.
%K A258486 nonn
%O A258486 1,3
%A A258486 _Sara Billey_, May 31 2015