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A349328
Number of polyominoes with n cells and exactly one line of reflection symmetry, where that one line is parallel to the grid and passes through the center of at least one square.
5
0, 0, 0, 1, 2, 4, 9, 16, 38, 62, 147, 241, 564, 926, 2148, 3561, 8195, 13700, 31349, 52858, 120357, 204444, 463712, 792986, 1792582, 3083469, 6950579, 12018394, 27023509, 46943409, 105320716, 183715445, 411364068, 720236762, 1609836928, 2828102115
OFFSET
1,5
LINKS
FORMULA
For odd n, a(n) = A006746(n).
For even n, a(n) = A006746(n) - A349329(n/2).
EXAMPLE
a(4) is 1 because of the tetromino:
O
OOO
CROSSREFS
Sequences classifying polyominoes by symmetry group: A000105, A006746, A006747, A006748, A006749, A056877, A056878, A142886, A144553, A144554, A349329.
Sequence in context: A282776 A283015 A264629 * A358904 A283059 A283081
KEYWORD
nonn
AUTHOR
John Mason, Nov 15 2021
STATUS
approved