A346736 - OEIS

A346736

Number of configurations of the 7 X 2 variant of the sliding block 15-puzzle that require a minimum of n moves to be reached, starting with the empty square in one of the corners.

1, 2, 3, 6, 11, 20, 37, 67, 117, 198, 329, 557, 942, 1575, 2597, 4241, 6724, 10535, 16396, 25515, 39362, 60532, 92089, 138969, 207274, 307725, 453000, 664240, 964874, 1392975, 1992353, 2832063, 3988528, 5586275, 7756511, 10698721, 14621717, 19840724, 26676629

(list; graph; refs; listen; history; text; internal format)

OFFSET

0,2

COMMENTS

This sequence was originally computed by Richard Korf, but the full sequence was not included in his paper. It was later re-computed by Tomas Rokicki.

LINKS

Ben Whitmore, Table of n, a(n) for n = 0..108

Richard Korf, Linear-time Disk-Based Implicit Graph Search, Journal of the ACM 55 (2008), No. 6.

Tomas Rokicki, Twenty-Four puzzle, some observations, 2011.

EXAMPLE

Starting from the solved configuration

1 2 3 4 5 6 7

8 9 10 11 12 13

the unique configuration requiring 108 moves is

7 6 12 4 3 9 1

13 5 11 10 2 8

PROG