OFFSET
0,2
FORMULA
For n>=27 all terms are 0 as the walk contains more steps than there are available lattice points in the 2x2x2 box.
EXAMPLE
a(1) = 4 as the walk is free to move one step in four directions.
a(2) = 12. A first step along either edge leading to the corner leaves two possible second steps. A first step to the centre of either face can be followed by a second step to three edges or to the center of the cube, four steps in all. Thus the total number of 2-step walks is 2*2+2*4 = 12.
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's edge.
CROSSREFS
KEYWORD
nonn,walk,fini,full
AUTHOR
Scott R. Shannon, Aug 14 2020
STATUS
approved