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%I #13 Sep 08 2019 11:46:53
%S 3,2,5,22,123,800,5754,44514,363893,3106288,27457050,249768040,
%T 2327398572,22135606604,214270565106,2106151496858,20982672402385,
%U 211545853142240,2155553788108702,22174250217880984,230075164780356214
%N Number of ways a loop can cross two parallel roads 2n times.
%C There is no obligation to cross the lower road (cf. A077054).
%F a(n) = A077054(n) + A005315(n) for n >= 1. - _Andrew Howroyd_, Nov 26 2015
%t A005315 = Cases[Import["https://oeis.org/A005315/b005315.txt", "Table"], {_, _}][[All, 2]];
%t A005316 = Cases[Import["https://oeis.org/A005316/b005316.txt", "Table"], {_, _}][[All, 2]];
%t a[n_] := If[n == 0, 3, A005315[[n + 1]] + A005316[[2 n + 1]]];
%t a /@ Range[0, 20] (* _Jean-François Alcover_, Sep 08 2019 *)
%Y Cf. A077054, A086031.
%K nonn
%O 0,1
%A _N. J. A. Sloane_ and _Jon Wild_, Aug 25 2003
%E a(13)-a(20) from _Andrew Howroyd_, Nov 26 2015
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