This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A337021 #14 Aug 16 2020 14:07:58 %S A337021 1,6,24,72,168,456,1032,2712,5784,14640,29760,71136,133344,291696, %T A337021 479232,950880,1343088,2375808,2774832,4266240,3909792,5046672, %U A337021 3230400,3316704,1122000,808128,0 %N A337021 The number of n-step self avoiding walks on a 3D cubic lattice confined inside a box of size 2x2x2 where the walk starts at the center of the box. %F A337021 For n>=27 all terms are 0 as the walk contains more steps than there are available lattice points in the 2x2x2 box. %e A337021 a(1) = 6 as the walk is free to move one step in all six axial directions. %e A337021 a(2) = 24 as after a step in one of the six axial directions the walk must turn along the face of the box; this eliminates the 2-step straight walk in all directions, so the total number of walks is 6*5-6 = 24. %e A337021 a(26) = 0 as it is not possible to visit all 26 available lattice points when the walk starts from the middle of the box. %Y A337021 Cf. A337023 (other box sizes), A337033 (start at center of face), A335806 (start at middle of edge), A337034 (start at corner of box), A001412, A039648. %K A337021 nonn,walk %O A337021 0,2 %A A337021 _Scott R. Shannon_, Aug 11 2020