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A146050
Number of n X n binary arrays symmetric about both diagonal and antidiagonal with all ones connected only in a 2X2 block with tail 1,1 1,2 1,3 2,2 2,3 in any orientation.
0
1, 1, 1, 1, 1, 3, 9, 19, 37, 115, 481, 2395, 10969, 57003, 371055, 2992969, 26653005, 266091447, 3019768963, 42043911685, 666291390951, 12240477419651, 251570549673017, 6156133419360705, 172490682719945137
OFFSET
1,6
EXAMPLE
Maximal 8 X 8 example
.0.0.0.0.1.1.0.0
.0.0.0.0.1.1.0.0
.0.0.0.0.1.0.1.1
.0.0.0.0.0.1.1.1
.1.1.1.0.0.0.0.0
.1.1.0.1.0.0.0.0
.0.0.1.1.0.0.0.0
.0.0.1.1.0.0.0.0
CROSSREFS
Sequence in context: A294367 A339495 A146694 * A147500 A300445 A115238
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 26 2008
STATUS
approved