A145815 - OEIS

A145815

1/4 of the number of islands of ones fitting in an n X n array symmetric about the diagonal and under 90-degree rotation with all ones connected only either three adjacent vertically or three adjacent horizontally.

%I #5 Nov 25 2018 12:22:16

%S 0,0,0,0,1,0,1,0,3,2,4,4,6,4,7,6,10,8,12,12,15,14,19,16,22,20,26,24,

%T 31,28

%N 1/4 of the number of islands of ones fitting in an n X n array symmetric about the diagonal and under 90-degree rotation with all ones connected only either three adjacent vertically or three adjacent horizontally.

%e 9 X 9 example with 12 islands:

%e 0 1 1 1 0 1 1 1 0

%e 1 0 0 0 0 0 0 0 1

%e 1 0 0 1 1 1 0 0 1

%e 1 0 1 0 0 0 1 0 1

%e 0 0 1 0 0 0 1 0 0

%e 1 0 1 0 0 0 1 0 1

%e 1 0 0 1 1 1 0 0 1

%e 1 0 0 0 0 0 0 0 1

%e 0 1 1 1 0 1 1 1 0

%K nonn

%O 1,9

%A _R. H. Hardin_, Oct 20 2008