Robot Walks

Show HTML problem contentShow HTML problem content  Published on Friday, 12th September 2008, 02:00 pm; Solved by 1593;
Difficulty rating: 70%

Problem 208

A robot moves in a series of one-fifth circular arcs (72°), with a free choice of a clockwise or an anticlockwise arc for each step, but no turning on the spot.

One of 70932 possible closed paths of 25 arcs starting northward is

Given that the robot starts facing North, how many journeys of 70 arcs in length can it take that return it, after the final arc, to its starting position?
(Any arc may be traversed multiple times.)