

A007834


Number of point labeled reduced 5free twographs with n nodes.


0



1, 0, 1, 1, 16, 76, 1016, 10284, 157340, 2411756, 44953712, 899824256, 20283419872, 495216726096, 13202082981712, 378896535199888, 11690436112988224, 385173160930360192, 13509981115738946816
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,5


LINKS

Table of n, a(n) for n=1..19.
P. J. Cameron, Counting twographs related to trees, Elec. J. Combin., Vol. 2, #R4.


FORMULA

E.g.f.: 2*LambertW(1/2*exp(1/2)*(1+x)^(1/2))/(1+x).  Vladeta Jovovic, Aug 21 2006
a(n) ~ sqrt(2)*sqrt(4exp(1)) * n^(n1) / (8*exp(n1)*(4*exp(1)1)^n).  Vaclav Kotesovec, Sep 30 2013


MATHEMATICA

CoefficientList[Series[2*LambertW[1/2*E^(1/2)*(1+x)^(1/2)]/(1+x), {x, 0, 15}], x]* Range[0, 15]! (* Vaclav Kotesovec, Sep 30 2013 *)


CROSSREFS

Sequence in context: A118532 A253691 A300919 * A228741 A200873 A082966
Adjacent sequences: A007831 A007832 A007833 * A007835 A007836 A007837


KEYWORD

nonn


AUTHOR

Peter J. Cameron


STATUS

approved



