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%I #9 May 07 2019 23:13:56
%S 2,4,7,8,11,13,16,18,21,22,25,27,30,33,35,38,39,42,44,47,48,51,53,56,
%T 59,61,64,65,68,70,73,75,78,79,82,84,87,90,92,95,96,99,101,104,106,
%U 109,110,113,115,118,121,123,126,127,130,132,135,136,139,141,144,147,149,152,153,156,158,161,163,166,167,170,172
%N Indices of 3's in A305389.
%H Robert Israel, <a href="/A316326/b316326.txt">Table of n, a(n) for n = 1..10000</a>
%p f:= 'f':
%p f(1):= 2: f(2):= 3: f(3):= (1,2,3):
%p S:= [1];
%p for i from 1 to 5 do T:= map(f,S); U:= map(f,T); S:= map(f,U); od:
%p select(t -> S[t+1]=3, [$0..nops(S)-1]); # _Robert Israel_, May 07 2019
%Y Cf. A305389.
%Y A316324, A316325, A316326 have the same relation to A305389 as A003144, A003145, A003146 do to the ternary tribonacci word A080843 (or A092782).
%K nonn
%O 1,1
%A _N. J. A. Sloane_, Jul 09 2018