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Number of disconnected 5-regular (quintic) graphs on 2n vertices.
12

%I #25 Mar 12 2020 23:13:55

%S 0,0,0,0,0,0,1,3,66,8029,3484760,2595985770,2815099031417,

%T 4230059694039460,8529853839173455678,22496718465713456081402,

%U 75951258300080722467845995,322269241532759484921710401976

%N Number of disconnected 5-regular (quintic) graphs on 2n vertices.

%H N. J. A. Sloane, <a href="/transforms.txt">Transforms</a>

%H Jason Kimberley, <a href="/wiki/User:Jason_Kimberley/A068933">Disconnected regular graphs (with girth at least 3)</a>

%H Jason Kimberley, <a href="/wiki/User:Jason_Kimberley/D_k-reg_girth_ge_g_index">Index of sequences counting disconnected k-regular simple graphs with girth at least g</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/DisconnectedGraph.html">Disconnected Graph</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/QuinticGraph.html">Quintic Graph</a>

%F a = A165626 - A006821 = Euler_transformation(A006821) - A006821.

%F a(n)=A068933(2n,5).

%Y 5-regular simple graphs: A006821 (connected), this sequence (disconnected), A165626 (not necessarily connected).

%Y Disconnected regular simple graphs: A068932 (any degree), A068933 (triangular array), specified degree k: A165652 (k=2), A165653 (k=3), A033483 (k=4), this sequence (k=5), A165656 (k=6), A165877 (k=7), A165878 (k=8), A185293 (k=9), A185203 (k=10), A185213 (k=11).

%K nonn,hard,more

%O 0,8

%A _Jason Kimberley_, Sep 28 2009

%E Terms a(13)-a(17), due to the extension of A006821 by _Andrew Howroyd_, from _Jason Kimberley_, Mar 12 2020