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A050998
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Lexicographically earliest solution to Langford (or Langford-Skolem) problem of arranging the numbers 1,1,2,2,3,3,...,n,n so that there is one number between the two 1's, two numbers between the two 2's, ..., n numbers between the two n's.
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4
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231213, 23421314, 14156742352637, 14167345236275, 15146735423627, 15163745326427, 15167245236473, 15173465324726, 16135743625427, 16172452634753, 17125623475364, 17126425374635, 23627345161475
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Entries are indexed by numbers n == -1 or 0 mod 4 (A014601).
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REFERENCES
| M. Gardner, Mathematical Magic Show, New York: Vintage, pp. 70 and 77-78, 1978.
R. K. Guy, `The unity of combinatorics', Proc. 25th Iranian Math. Conf, Tehran, (1994), Math. Appl 329 129-159, Kluwer Dordrecht 1995, Math. Rev. 96k:05001.
C. D. Langford, Math. Gaz., 1958, vol. 42, p. 228.
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LINKS
| More information
Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.
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CROSSREFS
| See A014552 (the main entry for this problem) for number of solutions.
Sequence in context: A139411 A015319 A179624 * A128484 A116463 A015331
Adjacent sequences: A050995 A050996 A050997 * A050999 A051000 A051001
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KEYWORD
| nonn,nice,easy
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AUTHOR
| Eric Weisstein (eric(AT)weisstein.com)
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