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A141582
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a(n)= number of ways to dispose two pawns on a chessboard of size n X n (two dispositions are equivalent if one can be rotated or reflected to give the other one).
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0
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2, 8, 21, 48, 93, 168, 278, 440, 660, 960, 1347, 1848, 2471, 3248, 4188, 5328, 6678, 8280, 10145, 12320, 14817, 17688, 20946, 24648, 28808, 33488, 38403, 44520, 50955, 58080, 65912, 74528, 83946, 94248
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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FORMULA
| For n even, a(n) = n * (n^3 + 6*n -4) / 16 for n odd a(n) = (n^2-1) * (n^2 + 7) / 16
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EXAMPLE
| For n = 2, two ways : either two pawns on any edge, or two pawns on any diagonal, hence a(2)=2
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CROSSREFS
| Sequence in context: A090612 A051744 A062443 * A192692 A182704 A000160
Adjacent sequences: A141579 A141580 A141581 * A141583 A141584 A141585
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KEYWORD
| easy,nonn
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AUTHOR
| Philippe Lallouet (philip.lallouet(AT)orange.fr), Aug 19 2008
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