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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

Table of n, a(n) for n=1..26.

Index entries for sequences related to trees

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

N. J. A. Sloane.

EXTENSIONS

More terms (from Dobrynin/Mel'nikov reference), Jernej Azarija, Aug 13 2012.

STATUS

approved

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Last modified June 26 04:02 EDT 2019. Contains 324368 sequences. (Running on oeis4.)