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Search: id:A141057
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| A141057 |
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Number of Abelian cubes of length 3n over an alphabet of size 3. An Abelian cube is a string of the form x x' x'' with |x| = |x'| = |x''| and x is a permutation of x' and x''. |
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1
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| 1, 3, 27, 381, 6219, 111753, 2151549, 43497891, 912018123, 19671397617, 434005899777, 9754118112951, 222621127928109
(list; graph; listen)
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OFFSET
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1,2
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FORMULA
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a(n) = sum of (n!/(n1)! (n2)! (n3!))^3 over all nonnegative n1, n2, n3 such that n1+n2+n3 = n.
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EXAMPLE
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a(1) = 3 as the Abelian cubes are aaa, bbb, ccc.
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CROSSREFS
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Sequence in context: A067000 A157089 A138436 this_sequence A011781 A094577 A108525
Adjacent sequences: A141054 A141055 A141056 this_sequence A141058 A141059 A141060
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KEYWORD
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nonn
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AUTHOR
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Jeffrey Shallit (shallit(AT)cs.uwaterloo.ca), Aug 01 2008
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