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%I #15 Jan 01 2019 06:31:05
%S 1,13,85,673,5021,38237,289089,2191309,16594837,125714929,952245373,
%T 7213225309,54639088433,413885098253,3135127983381,23748220228801,
%U 179889887447581,1362644200671133,10321865130390817
%N Number of 2-factors in W_4 X P_n.
%D F. Faase, On the number of specific spanning subgraphs of the graphs G X P_n, Ars Combin. 49 (1998), 129-154.
%H F. Faase, <a href="http://www.iwriteiam.nl/Cpaper.zip">On the number of specific spanning subgraphs of the graphs G X P_n</a>, Preliminary version of paper that appeared in Ars Combin. 49 (1998), 129-154.
%H F. Faase, <a href="http://www.iwriteiam.nl/counting.html">Counting Hamiltonian cycles in product graphs</a>
%H F. Faase, <a href="http://www.iwriteiam.nl/Cresults.html">Results from the counting program</a>
%F a(1) = 1,
%F a(2) = 13,
%F a(3) = 85,
%F a(4) = 673,
%F a(5) = 5021 and
%F a(n) = 6a(n-1) + 16a(n-2) - 29a(n-3) - 16a(n-4) + 16a(n-5).
%F G.f.: x(1+7x-9x^2-16x^3+16x^4)/(1-6x-16x^2+29x^3+16x^4-16x^5). [From _R. J. Mathar_, Dec 16 2008]
%K nonn
%O 1,2
%A _Frans J. Faase_
%E Added recurrence from Faase's web page. - _N. J. A. Sloane_, Feb 03 2009
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