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%I #21 Jan 16 2018 03:04:26
%S 1,2,2,4,10,36,188,1582,20576,388592,10461898,408377408,23652253982,
%T 2052824036762,265634749049320,50828371798067240,14332652975511249270,
%U 5965063285700860583374,3673747085941764271303790,3352654279654465148964378096
%N Number of 'zig-zag' self-avoiding walks on an n X n lattice from a corner to opposite one.
%C A 'zig-zag' walk does not contain 2 consecutive steps in the same direction.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Self-AvoidingWalk.html">Self-avoiding walk.</a>
%e a(4)=4 because of the following paths:
%e A._......A......A.._.......A_
%e ...|_....|_.....|_|.|_......_|
%e .....|_....|_........_|....|_..._
%e .......|.....|_.....|_.......|_|.|
%e .......B.......B......B..........B
%Y Cf. A034166.
%K nonn,walk
%O 1,2
%A _Felice Russo_
%E a(7)-a(11) computed by _David W. Wilson_
%E a(12)-a(13) computed by _Luca Petrone_, Dec 31 2015
%E a(14)-a(20) from _Andrew Howroyd_, Jan 15 2018
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