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%I #15 Nov 19 2014 08:39:44
%S 5,2100,457712,112269228,28477328812,7318410460100,1890316186147022,
%T 488986474759870194,126570653719713453566,32767699501924700122356,
%U 8483817993681247935283336,2196573666944370207848161336,568727175315063817973036015946
%N Number of paths joining opposite corners of an n X 4 grid with every vertex appearing at most twice in the path.
%C Limit n->infinity a(n)^(1/n) = 258.91660336499804152326399147605283475710016... . - _Vaclav Kotesovec_, Nov 19 2014
%H Muhammad Kholilurrohman, <a href="/A247106/b247106.txt">Table of n, a(n) for n = 1..100</a>
%e For n = 1 corresponds to a straight line graph with vertices {1,2,3,4}. Then the a(1) = 5 solutions are 1234, 121234, 123234, 123434, and 12123434.
%Y Cf. A239688, A247070.
%K nonn
%O 1,1
%A _Muhammad Kholilurrohman_, Nov 18 2014