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, 1, 1, 1, 0, 7, 8, 22, 25, 66, 73, 204, 231, 513, 576, 1520, 1715, 3763, 4085

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.

Links

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

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

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