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%I #13 Nov 16 2015 04:25:16
%S 6,472,14508,616945,23310528,919890493,35726458296,1395733639864,
%T 54409227545670,2122708670082349,82790398883086464,
%U 3229363021350300853,125961061338940140882,4913174522492216122360,191639794681507592618832,7474980745741030831444357,291564159140628690376670784,11372562031468273218156678121,443590715863319911428764167260,17302409958226333533759796319896
%N Number of perfect matchings in the graph Petersen X P_n.
%H Andrew Howroyd, <a href="/A220865/b220865.txt">Table of n, a(n) for n = 1..30</a>
%H S. Butler and S. Osborne, <a href="http://orion.math.iastate.edu/butler/papers/14_02_walks.pdf">Counting tilings by taking walks</a>, 2012.
%K nonn
%O 1,1
%A _N. J. A. Sloane_, Dec 27 2012
%E a(8)-a(20) from _Andrew Howroyd_, Nov 15 2015