A212807 Number of ways to place 2n points on a 2n X 2n square array of points such that no three points are collinear and the configuration has 90-degree rotational symmetry.

1, 1, 3, 4, 7, 4, 13, 13, 7, 16, 8, 23, 36, 58, 92, 101, 172, 281, 337, 541, 746

Offset

1,3

Comments

No such arrangement is possible on a 2n+1 X 2n+1 grid.

Links

Table of n, a(n) for n=1..21.

D. B. Anderson, Sample solutions for n = 18, 20, 22, 24, 26

David Brent Anderson Update on the no-three-in-line problem, J. Combin. Theory Ser. A 27 (1979), no. 3, 365--366. MR0555806(81g:05055).

A. Flammenkamp, Solutions of the no-three-in-line problem

Crossrefs

Cf. A000769.

Sequence in context: A337124 A267447 A071051 * A163830 A254931 A338285

Adjacent sequences: A212804 A212805 A212806 * A212808 A212809 A212810

Keyword

nonn,more,fini

Author

N. J. A. Sloane, May 29 2012

Extensions

a(11)-a(21) from Giovanni Resta, Mar 22 2013 (data from A. Flammenkamp's website)

Status

approved