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This is the number of positions that can be reached in n moves from the start, but which cannot be reached in fewer than n moves.
A puzzle in the Rubik cube family. The total number of distinct positions is 2401. Here positions differing by rotations or reflections are considered distinct.
Table of n, a(n) for n=0..24.
Jaap Scherphuis, Puzzle Pages
Sequence in context: A137035 A137042 A080546 * A259583 A064349 A101965
Adjacent sequences: A080551 A080552 A080553 * A080555 A080556 A080557
N. J. A. Sloane, Feb 21 2003