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A362709
a(n) is the number of almost almost unitary polyominoes of size n. An almost almost unitary polyomino is one in which all but 2 of its perimeter walls have length 1.
1
0, 1, 2, 2, 4, 12, 15, 29, 58, 116, 199, 403, 790, 1509, 2857, 5700, 10941, 21032
OFFSET
1,3
EXAMPLE
a(4)=2 because of:
O O
O OO
O O
O
CROSSREFS
Sequence in context: A353131 A134435 A136718 * A112362 A134720 A019225
KEYWORD
nonn,hard,more
AUTHOR
John Mason, Apr 30 2023
STATUS
approved