%I A050998
%S A050998 231213,23421314,14156742352637,14167345236275,15146735423627,
%T A050998 15163745326427,15167245236473,15173465324726,16135743625427,
%U A050998 16172452634753,17125623475364,17126425374635,23627345161475
%N A050998 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.
%C A050998 Entries are indexed by numbers n == -1 or 0 mod 4 (A014601).
%D A050998 M. Gardner, Mathematical Magic Show, New York: Vintage, pp. 70 and 77-78, 
               1978.
%D A050998 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.
%D A050998 C. D. Langford, Math. Gaz., 1958, vol. 42, p. 228.
%H A050998 <a href="http://www.lclark.edu/~miller/langford.html">More information</
               a>
%H A050998 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               LangfordsProblem.html">Link to a section of The World of Mathematics.</
               a>
%Y A050998 See A014552 (the main entry for this problem) for number of solutions.
%Y A050998 Sequence in context: A061134 A139411 A015319 this_sequence A128484 A116463 
               A015331
%Y A050998 Adjacent sequences: A050995 A050996 A050997 this_sequence A050999 A051000 
               A051001
%K A050998 nonn,nice,easy
%O A050998 1,1
%A A050998 Eric Weisstein (eric(AT)weisstein.com)