%I #9 Jun 20 2016 10:15:26
%S 121,123,141,142,0,121121,121123,121141,121142,0,123121,123123,123141,
%T 123142,0,141121,141123,141141,141142,0,142121,142123,142141,142142,0,
%U 0,0,0,0,0,121121121,121121123,121121141,121121142,0,121123121,121123123,121123141
%N a(n) = n base 5, under morphism f(1) = 121, f(2) = 123, f(3) = 141, f(4) = 142, or 0 if n base 5 has a zero.
%H James Currie, Narad Rampersad, <a href="http://arXiv.org/abs/0806.0044">Dejean's conjecture holds for n >= 30</a>, arXiv:0806.0044 [math.NT], May 30 2008.
%F a(n) = A007091(n) under the morphism f(1) = 121, f(2) = 123, f(3) = 141, f(4) = 142, or 0 if n base 5 is not a word in the alphabet {1,2,3,4}* i.e., has a zero.
%t a[n_] := Block[{d = IntegerDigits[n, 5]}, If[Min[d] == 0, 0, FromDigits[ Flatten[d /. {1 > {1,2,1}, 2 > {1,2,3}, 3 > {1,4,1}, 4 > {1,4,2}}]]]]; Array[a, 38] (* _Giovanni Resta_, Jun 20 2016 *)
%Y Cf. A007091.
%K base,easy,nonn
%O 1,1
%A _Jonathan Vos Post_, Jun 03 2008
%E Data corrected by _Giovanni Resta_, Jun 20 2016
