%I A051041
%S A051041 4,12,36,96,264,696,1848,4848,12768,33480,87936,230520,604608,1585128,
%T A051041 4156392,10895952,28566216,74887056,196322976,514662960,1349208600,
%U A051041 3536962584,9272217936,24307198464,63721617888
%N A051041 Number of square-free quaternary words of length n.
%H A051041 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               SquarefreeWord.html">Link to a section of The World of Mathematics.</
               a>
%Y A051041 Cf. A006156.
%Y A051041 Sequence in context: A020875 A063810 A002842 this_sequence A002906 A001411 
               A095350
%Y A051041 Adjacent sequences: A051038 A051039 A051040 this_sequence A051042 A051043 
               A051044
%K A051041 nonn
%O A051041 1,1
%A A051041 Eric Weisstein (eric(AT)weisstein.com)
%E A051041 More terms from David Wasserman (wasserma(AT)spawar.navy.mil), Feb 27 
               2002
%E A051041 a(13)-a(15) from John W. Layman (layman(AT)math.vt.edu), Mar 03 2004
%E A051041 a(16)-a(25) from Max Alekseyev (maxale(AT)gmail.com), Jul 03 2006