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A007834 Number of point labeled reduced 5-free two-graphs with n nodes. 0

%I

%S 1,0,1,1,16,76,1016,10284,157340,2411756,44953712,899824256,

%T 20283419872,495216726096,13202082981712,378896535199888,

%U 11690436112988224,385173160930360192,13509981115738946816

%N Number of point labeled reduced 5-free two-graphs with n nodes.

%H P. J. Cameron, <a href="http://www.combinatorics.org/Volume_2/volume2.html#R4">Counting two-graphs related to trees</a>, Elec. J. Combin., Vol. 2, #R4.

%F E.g.f.: -2*LambertW(-1/2*exp(-1/2)*(1+x)^(1/2))/(1+x). - _Vladeta Jovovic_, Aug 21 2006

%F a(n) ~ sqrt(2)*sqrt(4-exp(1)) * n^(n-1) / (8*exp(n-1)*(4*exp(-1)-1)^n). - _Vaclav Kotesovec_, Sep 30 2013

%t 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 *)

%K nonn

%O 1,5

%A _Peter J. Cameron_

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Last modified January 22 07:39 EST 2020. Contains 331139 sequences. (Running on oeis4.)