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A007141 E-trees with at most 2 colors.
(Formerly M1757)
3
1, 2, 7, 22, 75, 250, 886, 3150, 11525, 42698, 160636, 610694, 2345584, 9081850, 35422281, 139022744, 548671671, 2176051206, 8668363781, 34667284600, 139140831224, 560271494924, 2262709876353, 9163000968906, 37198940600718, 151364381619042 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

REFERENCES

G. Gati, F. Harary and R. W. Robinson, Line colored trees with extendable automorphisms, Acta Math. Scientia, 2 (1982), 105-110.

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

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

G. Gati, F. Harary, R. W. Robinson, Line colored trees with extendable automorphisms, Acta Mathematica Scientia 2.1 (1982), 105-110. (Annotated scanned copy)

Index entries for sequences related to trees

FORMULA

a(n) = E(2, n) where E(c, 1) = 1, E(c, n) = (1/(n-1)) * Sum_{i=1..n-1} ((c+1) * i - n + 1) * S(c, i) * E(c, n-i) and S(c, 0) = 1 and S(c, n) = Sum_{d | n} E(c, d) [From Gati, Harary, Robinson]. - Sean A. Irvine, Oct 29 2017

CROSSREFS

Sequence in context: A137398 A151439 A204218 * A278151 A090831 A174403

Adjacent sequences:  A007138 A007139 A007140 * A007142 A007143 A007144

KEYWORD

nonn

AUTHOR

N. J. A. Sloane.

EXTENSIONS

More terms from Sean A. Irvine, Oct 29 2017

STATUS

approved

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Last modified January 15 20:47 EST 2019. Contains 319184 sequences. (Running on oeis4.)