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%I #13 Apr 03 2018 10:13:18
%S 0,1,13,139,1605,20741
%N a(n) = number of edges in a cocoon concertina n-cube.
%C n-place formulas in first-order logic like Ax Ey P(x, y) or Ex P(x, x) can be ordered by implication. This Hasse diagram has A300696(n) vertices and a(n) edges.
%C The corresponding sequence for convex concertina n-cubes is A300693.
%H Tilman Piesk, <a href="https://en.wikiversity.org/wiki/Formulas_in_predicate_logic">Formulas in predicate logic</a> (Wikiversity)
%H Tilman Piesk, <a href="https://commons.wikimedia.org/wiki/File:Cocoon_concertina_square_graph.svg">Image of a cocoon concertina square</a> with 13 edges
%H Tilman Piesk, <a href="https://github.com/watchduck/concertina_hypercubes/tree/master/computed_results/cocoon/hasse">Lists of edges</a> for n=2..5
%H Tilman Piesk, <a href="https://github.com/watchduck/concertina_hypercubes/blob/master/cocoon.py">Python code used to generate the sequence</a>
%e The cocoon concertina square has the A300693(2) = 6 outer and 7 inner edges, giving a(n) = 13 in total.
%Y Cf. A300696, A300693.
%K nonn,more
%O 0,3
%A _Tilman Piesk_, Mar 24 2018
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