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A118644
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Number of distinct (n red, n blue, n green)-bead necklaces.
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0
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2, 16, 188, 2896, 50452, 953056, 19003476, 394397776, 8439756848, 185033251616, 4137181680700, 94020327215200, 2166105078791448, 50489825388328608, 1188777328563914488, 28236363841989180496
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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FORMULA
| Sum_{d|n} ( phi(n/d)(3d Choose d)(2d Choose d) )/3n [Corrected by several correspondents, Mar 04 2010]
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MATHEMATICA
| f[n_] := Plus @@ (EulerPhi[n/# ]Binomial[3#, # ]Binomial[2#, # ] & /@ Divisors[n])/(3n)
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CROSSREFS
| Cf. A003239.
Sequence in context: A052606 A011553 A123898 * A183205 A006335 A051711
Adjacent sequences: A118641 A118642 A118643 * A118645 A118646 A118647
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KEYWORD
| easy,nonn
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AUTHOR
| Jacob Siehler (siehlerj(AT)wlu.edu), May 10 2006
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