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A327638 a(0)=1, a(1)=5; for n > 2, a(n) is the smallest odd number j not divisible by 3 such that (3*j+1)/2^k = a(n-1) for some k.

%I A327638 #38 Nov 11 2020 20:27:48
%S A327638 1,5,13,17,11,7,37,49,65,43,229,305,203,541,721,961,5125,6833,4555,
%T A327638 6073,32389,172741,230321,153547,818917,4367557,5823409,7764545,
%U A327638 5176363,6901817,18404845,98159173,523515589,2792083141,3722777521,19854813445,105892338373
%N A327638 a(0)=1, a(1)=5; for n > 2, a(n) is the smallest odd number j not divisible by 3 such that (3*j+1)/2^k = a(n-1) for some k.
%C A327638 Also a reverse Collatz sequence with odd numbers. - _Paul Conradi_, Oct 23 2020
%C A327638 Odd numbers in A225570. - _Michel Marcus_, Oct 24 2020
%H A327638 Michel Marcus, <a href="/A327638/b327638.txt">Table of n, a(n) for n = 0..295</a>
%F A327638 If a(n-1) == 1 (mod 3) then a(n) = (4*a(n-1)-1)/3 or (16*a(n-1)-1)/3, whichever value is not divisible by 3.
%F A327638 If a(n-1) == -1 (mod 3) then a(n) = (2*a(n-1)-1)/3 or a(n)=(8*a(n-1)-1)/3, whichever value is not divisible by 3.
%e A327638 a(0)=1, a(1)=5 by definition, then a(2) = (2*5-1)/3 or (8*5-1)/3; as (2*5-1)/3 is divisible by 3, a(2) = (8*5-1)/3 = 13.
%o A327638 (PARI) lista(nn) = {print1(1, ", ", 5); x = 5; for (n = 2, nn, if(x%3 == 1, x = (4*x-1)/3, x = (2*x-1)/3); if(x%3 == 0, x = 4*x + 1); print1(", ",  x)); } \\ _Jinyuan Wang_, Sep 21 2019
%Y A327638 Intersection of A005408 and A225570.
%K A327638 nonn
%O A327638 0,2
%A A327638 _Pierre CAMI_, Sep 20 2019
%E A327638 More terms from _Jinyuan Wang_, Sep 21 2019