Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%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