%I A059108
%S A059108 1,0,0,0,0,0,0,0,9,20,33,0,0,0,0,0,0,200343,869006,4247790
%N A059108 Number of solutions to variant of triples version of Langford (or Langford-Skolem) 
               problem.
%C A059108 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?
%H A059108 <a href="http://www.lclark.edu/~miller/langford.html">J. E. Miller, Langford's 
               Problem</a>
%Y A059108 Cf. A014552, A050998, A059106, A059107.
%Y A059108 Sequence in context: A050682 A094196 A017497 this_sequence A028566 A147479 
               A146680
%Y A059108 Adjacent sequences: A059105 A059106 A059107 this_sequence A059109 A059110 
               A059111
%K A059108 nonn,nice,hard
%O A059108 1,9
%A A059108 N. J. A. Sloane (njas(AT)research.att.com), Feb 14 2001