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A132220 Number of line graphs on n unlabeled nodes. 2
1, 2, 4, 10, 24, 63, 166, 471, 1408, 4436, 14719, 51468, 188754, 725010, 2907576, 12141462, 52654529, 236584104, 1098926868, 5266708497, 25997964452, 131975740172, 688019138485, 3678898458587, 20153878941460, 113000861804642, 647866385202660, 3794917399892511, 22693153274994534, 138436809489370914, 860962282687080614 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Max Alekseyev, Table of n, a(n) for n = 1..60

Eric Weisstein's World of Mathematics.  Line Graph.

FORMULA

For n>=3, a(n) = A000664(n) - A000664(n-3). - Max Alekseyev, Sep 03 2016

MATHEMATICA

<< Combinatorica`; With[{e = Table[NumberOfGraphs[2 n, n], {n, 12}]}, e - Join[{0, 0, 1}, Drop[e, -3]]] (* Eric W. Weisstein, Oct 30 2017 *)

<< Combinatorica`; With[{e = Table[Coefficient[GraphPolynomial[2 n, x], x, n], {n, 12}], e - Join[{0, 0, 1}, Drop[e, -3]]] (* Eric W. Weisstein, Oct 30 2017 *)

CROSSREFS

Euler transform of A003089.

Cf. A132219 (labeled case).

Sequence in context: A121691 A124499 A303840 * A007874 A294410 A121704

Adjacent sequences:  A132217 A132218 A132219 * A132221 A132222 A132223

KEYWORD

nonn

AUTHOR

Vladeta Jovovic, Aug 14 2007

EXTENSIONS

a(25)-a(60) from Max Alekseyev, Sep 07 2016

STATUS

approved

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Last modified July 25 02:57 EDT 2021. Contains 346282 sequences. (Running on oeis4.)