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%I #18 Nov 07 2020 09:41:27
%S 1,12,121,1211,12112,121121,1211212,12112121,121121211,1211212112,
%T 12112121121,121121211211,1211212112112,12112121121121,
%U 121121211211212,1211212112112121,12112121121121211,121121211211212112,1211212112112121121,12112121121121211212
%N a(n) = length-n prefix of the Fibonacci word A003842.
%H Alois P. Heinz, <a href="/A214317/b214317.txt">Table of n, a(n) for n = 1..300</a>
%p S:= proc(n) option remember;
%p `if`(n<2, [2-n], [S(n-1)[], S(n-2)[]])
%p end:
%p a:= proc(n) local k;
%p for k while nops(S(k))<n do od;
%p parse(cat(S(k)[1..n][]))
%p end;
%p seq(a(n), n=1..30); # _Alois P. Heinz_, Jul 19 2012
%t S = SubstitutionSystem[{1 -> {1, 2}, 2 -> {1}}, {1}, 20];
%t FromDigits[Take[#[[1]], #[[2]]]]& /@ Transpose[{S, Range[Length[S]]}] (* _Jean-François Alcover_, Nov 07 2020 *)
%Y Cf. A003842, A214318.
%K nonn
%O 1,2
%A _N. J. A. Sloane_, Jul 12 2012
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