A258251 Numbers n for which there exists a fixed point in the Collatz (3x+1) trajectory of n.

1, 4, 5, 9, 12, 13, 22, 23, 24, 26, 32, 33, 36, 37, 38, 49, 50, 51, 56, 58, 60, 61, 72, 74, 78, 79, 80, 86, 87, 105, 123, 124, 125, 126, 127, 130, 131, 132, 133, 134, 136, 138, 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

Offset

1,2

Comments

Numbers n such that A258772(n) > 0.

Links

Table of n, a(n) for n=1..70.

Example

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.
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.

Prog

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

Crossrefs

Cf. A258772, A006370, A070165.

Sequence in context: A269741 A047610 A126004 * A331086 A332020 A184801

Adjacent sequences: A258248 A258249 A258250 * A258252 A258253 A258254

Keyword

nonn

Author

Derek Orr, Jun 11 2015

Status

approved