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A280537 Maximum number of points that can be selected from an n X n X n grid so that no four of them are in a plane. 2
5, 8, 10, 13, 16, 18, 20 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

COMMENTS

Terms up to a(6) were found by exhaustive search. a(7) and a(8) are based on extensive numerical evidence.

Currently (January 2017) known lower bounds for the next terms are a(9)>=23, a(10)>=26, a(11)>=28, a(12)>=30, a(13)>=32, a(14)>=35, a(15)>=36, a(16)>=38, a(17)>=42.

REFERENCES

Walter Möhres, Exhaustive Search for the 6x6x6 "No Four in Plane Problem". Private communication, September 2016.

LINKS

Table of n, a(n) for n=2..8.

Ed Pegg Jr, No-Four-In-Plane Problem, Wolfram Demonstrations Project.

Ed Pegg, No-Four-In-Plane, can 11 points be picked from a 4 X 4 X 4 grid?. Question in Mathematics Stack Exchange, a(4) and a(5) provided in answers.

Torsten Sillke, no 4 on a plane (3*3*3 puzzle), discussion in newsgroup rec.puzzles, Nov 27, 1992.

Al Zimmermann's Programming Contests, Non-Coplanar Points, March - June 2016.

CROSSREFS

Cf. A000769, A272651, A280538.

Sequence in context: A325180 A087280 A335495 * A022413 A078781 A256359

Adjacent sequences:  A280534 A280535 A280536 * A280538 A280539 A280540

KEYWORD

nonn,more,hard

AUTHOR

Hugo Pfoertner, Jan 05 2017

STATUS

approved

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Last modified August 12 12:09 EDT 2020. Contains 336439 sequences. (Running on oeis4.)