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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
 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 0, 7, 8, 22, 25, 66, 73, 204, 231, 513, 576, 1520, 1715, 3763, 4085 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,13 REFERENCES A. A. Dobrynin (dobr(AT)math.nsc.ru), Distance of iterated line graphs, Graph Theory Notes of NY, 37 (1999), 8-9. 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 LINKS PROG (Sage) # needs the package nauty def a(n):     c = 0     for el in graphs.nauty_geng(str(n) + ' -c ' + str(n-1)+':' + str(n-1)):         g = (el.line_graph()).line_graph()         if el.wiener_index() == g.wiener_index():             c+=1     return c # Jernej Azarija, Aug 13 2012 CROSSREFS Sequence in context: A181585 A060291 A132899 * A322651 A325322 A288068 Adjacent sequences:  A051172 A051173 A051174 * A051176 A051177 A051178 KEYWORD nonn AUTHOR EXTENSIONS More terms (from Dobrynin/Mel'nikov reference), Jernej Azarija, Aug 13 2012 STATUS approved

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Last modified August 4 00:54 EDT 2020. Contains 336201 sequences. (Running on oeis4.)