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A187108 Odd numbers not in the trajectory of a smaller number under the Collatz (3x+1) iteration.

%I A187108 #19 Oct 07 2024 00:47:27
%S A187108 1,3,7,9,15,19,21,25,27,33,37,39,43,45,51,55,57,63,69,73,75,79,81,87,
%T A187108 93,97,99,105,109,111,115,117,123,127,129,133,135,141,145,147,151,153,
%U A187108 159,163,165,169,171,177,181,183,187,189,195,199,201,207,213,217
%N A187108 Odd numbers not in the trajectory of a smaller number under the Collatz (3x+1) iteration.
%C A187108 These are the odd numbers in A061641, which gives a more detailed explanation. - _T. D. Noe_, Mar 05 2011
%o A187108 (ActionScript) // AS3
%o A187108 var a:Array=new Array();
%o A187108 var i:int;
%o A187108 var n:int=0;
%o A187108 var ni:int;
%o A187108 var s:String='';
%o A187108 for (i=0;i<50;i++){
%o A187108 while(a[n]!=undefined) n++;
%o A187108 s+=String(2*n+1)+',';
%o A187108 a[n]=1;
%o A187108 ni=2*n+1;
%o A187108 while(ni>=2*n+1&&ni>1){
%o A187108 ni=3*ni+1;
%o A187108 while(ni%2==0)ni/=2;
%o A187108 a[(ni-1)/2]=1;
%o A187108 }
%o A187108 }
%o A187108 trace(s);
%Y A187108 Cf. A061641.
%K A187108 nonn
%O A187108 1,2
%A A187108 _Jimin Park_, Mar 05 2011