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A014409
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Number of inequivalent ways a pair of checkers can be placed on an n X n board.
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5
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0, 2, 8, 21, 49, 93, 171, 278, 446, 660, 970, 1347, 1863, 2471, 3269, 4188, 5356, 6678, 8316, 10145, 12365, 14817, 17743, 20946, 24714, 28808, 33566, 38703, 44611, 50955, 58185, 65912, 74648, 83946, 94384, 105453, 117801, 130853
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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REFERENCES
| Computed by Fred Hallden.
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FORMULA
| a(2n) = n/2 (2n^3 + 3n - 1); a(2n + 1) = n/2 (2n^3 + 4n^2 + 7n + 3)
a(n)=a(n-1)+3a(n-2)-3a(n-3)-3a(n-4)+3a(n-5)+a(n-6)-a(n-7) [From Kieren MacMillan (kieren(AT)alumni.rice.edu), Nov 08 2008]
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CROSSREFS
| Cf. A054252, A019318.
Sequence in context: A182704 A000160 A034519 * A109782 A123044 A143229
Adjacent sequences: A014406 A014407 A014408 * A014410 A014411 A014412
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KEYWORD
| nonn,nice,easy
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AUTHOR
| Borghard, William (bogey(AT)hostare.att.com)
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EXTENSIONS
| More terms and formula from Hugo van der Sanden (hv(AT)crypt.org)
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