A261212 Maximum number of 1's in an fully symmetrical n X n binary matrix with no three 1's adjacent in a line along a row, column or diagonally.

1, 4, 4, 8, 16, 20, 25, 36, 41, 48, 64, 72, 81, 100, 109, 120, 144, 156, 173, 196, 213, 228, 256, 272, 300, 324, 349, 368, 401, 424, 457, 484

Offset: 1

Author

V.J. Pohjola and Giovanni Resta, Aug 12 2015

Keywords

• nonn

Comments

Fully symmetrical refers to the four symmetry axes: horizontal, vertical and two diagonal.

Note that a(3k+2) = 4*(1+k)^2, for k=0,...,8, but a(29) = 401.

Examples

			For n=4, the matrix is
0 1 0
1 0 1
0 1 0
For n=6, the matrix is
1 1 0 0 1 1
1 0 1 1 0 1
0 1 0 0 1 0
0 1 0 0 1 0
1 0 1 1 0 1
1 1 0 0 1 1
		

Links

• Giovanni Resta, Illustration of a(6)-a(30)

Crossrefs

Cf. A181018.

Formula

a(n) <= A181018(n).

a(3k+2) >= 4*(k+1)^2.