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A059108
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Number of solutions to variant of triples version of Langford (or Langford-Skolem) problem.
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3
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1, 0, 0, 0, 0, 0, 0, 0, 9, 20, 33, 0, 0, 0, 0, 0, 0, 200343, 869006, 4247790
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,9
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COMMENTS
| How many ways are of arranging the numbers 1,1,1,2,2,2,3,3,3,...,n,n,n so that there are zero numbers between the first and second 1's and zero numbers between the second and third 1's; one number between the first and second 2's and one number between the second and third 2's; ... n-1 numbers between the first and second n's and n-1 numbers between the second and third n's?
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LINKS
| J. E. Miller, Langford's Problem
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CROSSREFS
| Cf. A014552, A050998, A059106, A059107.
Sequence in context: A050682 A094196 A017497 * A028566 A147479 A146680
Adjacent sequences: A059105 A059106 A059107 * A059109 A059110 A059111
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KEYWORD
| nonn,nice,hard
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Feb 14 2001
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