A258251 - OEIS

%I #21 Jun 16 2015 13:56:23

%S 1,4,5,9,12,13,22,23,24,26,32,33,36,37,38,49,50,51,56,58,60,61,72,74,

%T 78,79,80,86,87,105,123,124,125,126,127,130,131,132,133,134,136,138,

%U 140,141,153,156,157,158,160,168,170,192,196,197,198,200,202,204,205,206,207,217,224,232,233,234,241,246,247,249

%N Numbers n for which there exists a fixed point in the Collatz (3x+1) trajectory of n.

%C Numbers n such that A258772(n) > 0.

%e For n = 5, the trajectory is T(5) = [5, 16, 8, 4, 2, 1]. Since the fourth term in this sequence is 4, 5 has a fixed point. So 5 is a member of this sequence.

%e For n = 6, the trajectory is T(6) = [6, 3, 10, 5, 16, 8, 4, 2, 1]. Here, there is no fixed point and so, 6 is not a member of this sequence.

%o (PARI) Tvect(n)=v=[n]; while(n!=1, if(n%2, k=3*n+1; v=concat(v, k); n=k); if(!(n%2), k=n/2; v=concat(v, k); n=k)); v

%o m=1; while(m<10^3, d=Tvect(m); c=0; for(i=1, #d, if(d[i]==i, print1(m, ", "); break)); m++)

%Y Cf. A258772, A006370, A070165.

%K nonn

%O 1,2

%A _Derek Orr_, Jun 11 2015