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%I #41 Nov 19 2014 08:44:24
%S 3,218,9482,457712,22375458,1103498043,54446999831,2687689834743,
%T 132666417488114,6548713810387879,323256199668617476,
%U 15956549284724388645,787645179268653581373,38879655000676000582023,1919173045780901708089448
%N Number of paths joining opposite corners of an n X 3 grid with every vertex appearing at most twice in the path.
%C Limit n->infinity a(n)^(1/n) = 49.36188601343236732586002276917911067895959865... (root of polynomial of degree 50, see the denominator of generating function). - _Vaclav Kotesovec_, Nov 19 2014
%H Muhammad Kholilurrohman, <a href="/A247070/b247070.txt">Table of n, a(n) for n = 1..300</a>
%H Vaclav Kotesovec, <a href="/A247070/a247070_1.txt">Generating function and recurrence (of order 90)</a>
%e For n = 1 corresponds to a straight line graph with vertices {1,2,3}. Then the a(1) = 3 solutions are 123, 12123, and 12323.
%Y Cf. A239688, A247106.
%K nonn
%O 1,1
%A _Muhammad Kholilurrohman_, Nov 16 2014
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