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%I #17 Feb 26 2017 03:11:07
%S 1,1,2,16,4200,1093025200
%N Number of linear extensions for Young-Fibonacci lattices of increasing rank
%D Donald E. Knuth, The Art of Computer Programming, Volume 4 Fascicle 2, Generating All Tuples and Permutations (2005), v+128pp. ISBN 0-201-85393-0. [Algorithm V for generating all topological sorts.]
%H Frank Ruskey, <a href="http://theory.cs.uvic.ca/inf/pose/LinearExt.html">The Combinatorial Object Server (Implementation of Varol-Rotem algorithm)</a>.
%H Richard P. Stanley, <a href="https://doi.org/10.1090/S0894-0347-1988-0941434-9">Differential posets</a>, Journal of the American Mathematical Society Vol. 1, No. 4, pp. 919-961, 1988.
%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Young-Fibonacci_lattice">Young-Fibonacci lattice</a>
%e For n = 3, the Young-Fibonacci lattice as defined by the following edge set {(1,2),(2,3),(2,4)} has two total orderings: 1234 and 1243. The sequence increases rapidly since Young-Fibonacci lattices are sparse digraphs.
%K nonn,hard,more
%O 1,3
%A _Nikolaos Kavvadias_, Jan 23 2011
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