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A346035 a(1) = 1; if a(n) is not divisible by 3, a(n+1) = 4*a(n) + 1, otherwise a(n+1) = a(n)/3.

%I A346035 #45 Sep 27 2021 21:01:50
%S A346035 1,5,21,7,29,117,39,13,53,213,71,285,95,381,127,509,2037,679,2717,
%T A346035 10869,3623,14493,4831,19325,77301,25767,8589,2863,11453,45813,15271,
%U A346035 61085,244341,81447,27149,108597,36199,144797,579189,193063,772253,3089013,1029671,4118685
%N A346035 a(1) = 1; if a(n) is not divisible by 3, a(n+1) = 4*a(n) + 1, otherwise a(n+1) = a(n)/3.
%H A346035 Tristan Young, <a href="/A346035/b346035.txt">Table of n, a(n) for n = 1..15000</a>
%H A346035 Tristan Young, <a href="/A346035/a346035_1.c.txt">C code to generate a b-file for the first 15000 terms of this sequence</a>
%t A346035 a[1] = 1; a[n_] := a[n] = If[Divisible[a[n-1],3], a[n-1]/3, 4*a[n-1]+1]; Array[a, 50] (* _Amiram Eldar_, Jul 12 2021 *)
%o A346035 (Processing)
%o A346035 // generates all the numbers in the sequence before it first surpasses 1 billion
%o A346035 int n;
%o A346035 void setup() {
%o A346035   n = 1;
%o A346035   noLoop();
%o A346035 }
%o A346035 void draw() {
%o A346035   print(n + ",");
%o A346035   while (true) {
%o A346035     if (n % 3 == 0) {
%o A346035       n /= 3;
%o A346035     } else {
%o A346035       n *= 4; n++;
%o A346035     }
%o A346035     print(n);
%o A346035     if (n == 1 || n >= 600000000) {
%o A346035       break;
%o A346035     } else {
%o A346035       print(", ");
%o A346035     }
%o A346035   }
%o A346035 }
%o A346035 (PARI) a(n) = if (n==1, 1, my(x=a(n-1)); if (x % 3, 4*x+1, x/3)); \\ _Michel Marcus_, Aug 12 2021
%Y A346035 Cf. A006370, A128333, A153727.
%K A346035 easy,nonn
%O A346035 1,2
%A A346035 _Tristan Young_, Jul 02 2021