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A330280 Least number of 2 X 2 rotations required to solve an n X n Simon Tatham's Twiddle puzzle. 1
0, 2, 10, 24 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The puzzle is as follows. An n X n grid is filled with distinct integers from 1 to n*n, such that the number at row r and column c (both 0-based) is n*n - (r*n + c). The task is to perform rotations of 2 X 2 sub-grids (moves) to bring the numbers into their natural order, i.e., the number at row r and column c should become r*n + c + 1. Rotations are by 90 degrees in the clockwise or counterclockwise direction. See links for example puzzles and solutions.

Wladimir Leite found strong upper bounds for the next few terms: 48, 88 and 146 (see links). - Dmitry Kamenetsky, Apr 20 2020

LINKS

Table of n, a(n) for n=1..4.

greenturtle3141, What is the strategy to solve Simon Tatham's Twiddle?, Puzzling StackExchange, Dec 24 2016.

greenturtle3141, A Guide to the Number Rotation Puzzle, Puzzling StackExchange, May 27 2019.

Dmitry Kamenetsky, Rotating numbers in a 3x3 grid, Puzzling StackExchange, Feb 15 2020.

Dmitry Kamenetsky and Wladimir Leite, Best known solutions for 3 <= n <= 7

Simon Tatham, Twiddle 3x3 puzzle

Topcoder, Marathon Match 117 - RotatingNumbers

CROSSREFS

Sequence in context: A293403 A316451 A120845 * A293412 A224837 A049450

Adjacent sequences:  A330277 A330278 A330279 * A330281 A330282 A330283

KEYWORD

nonn,hard,more

AUTHOR

Dmitry Kamenetsky, Feb 29 2020

EXTENSIONS

Removed a(5) as it was found to be sub-optimal - Dmitry Kamenetsky, Apr 16 2020

STATUS

approved

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Last modified September 30 15:55 EDT 2020. Contains 337439 sequences. (Running on oeis4.)