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 A051175 Number of trees T of order n such that W(T) = W(L(L(T)) where W(G) and L(G) are the Wiener index and line graph of a graph G. 0

%I

%S 0,0,0,0,0,0,0,0,1,1,1,0,7,8,22,25,66,73,204,231,513,576,1520,1715,

%T 3763,4085

%N Number of trees T of order n such that W(T) = W(L(L(T)) where W(G) and L(G) are the Wiener index and line graph of a graph G.

%D A. A. Dobrynin (dobr(AT)math.nsc.ru), Distance of iterated line graphs, Graph Theory Notes of NY, 37 (1999), 8-9.

%D A. A. Dobrynin and L. S. Mel'nikov, Some results on the Wiener index of iterated line graphs, Electronic Notes in Discrete Mathematics 22 (2005), 469-475

%H <a href="/index/Tra#trees">Index entries for sequences related to trees</a>

%o (Sage) # needs the package nauty

%o def a(n):

%o c = 0

%o for el in graphs.nauty_geng(str(n) + ' -c ' + str(n-1)+':' + str(n-1)):

%o g = (el.line_graph()).line_graph()

%o if el.wiener_index() == g.wiener_index():

%o c+=1

%o return c

%o # _Jernej Azarija_, Aug 13 2012

%K nonn

%O 1,13

%A _N. J. A. Sloane_

%E More terms (from Dobrynin/Mel'nikov reference), _Jernej Azarija_, Aug 13 2012

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Last modified September 19 09:06 EDT 2020. Contains 337178 sequences. (Running on oeis4.)