A224540 Number of k such that all terms of the Collatz (3x+1) iteration of k are <= 3^n.

1, 2, 4, 12, 36, 106, 249, 613, 1732, 8028, 23348, 69370, 210807, 634839, 1893582, 5686389, 17031777, 51073675, 153185957, 459516225, 1378707224, 4135278456, 12406199367, 37216010685, 111651745638, 334951946950, 1004855123675, 3014552251123, 9043690122807

Offset

0,2

Links

Table of n, a(n) for n=0..28.

Carlo Corti, A224540: Computational extension through a(28) by truncated inverse Collatz-tree traversal, Zenodo archive, 2026.

Example

For n = 3, the twelve k are 1, 2, 3, 4, 5, 6, 8, 10, 12, 16, 20, and 24.

Mathematica

Collatz[n_] := NestWhileList[If[EvenQ[#], #/2, 3 # + 1] &, n, # > 1 &]; Table[Select[Range[3^n], Max[Collatz[#]] <= 3^n &], {n, 8}]

Crossrefs

Cf. A006884, A006885, A095384, A224538.

Sequence in context: A192236 A149839 A149840 * A025579 A214936 A010552

Adjacent sequences: A224537 A224538 A224539 * A224541 A224542 A224543

Keyword

nonn,more,changed

Author

T. D. Noe, Apr 24 2013

Extensions

a(20)-a(21) from Donovan Johnson, Jun 05 2013

a(22)-a(28) from Carlo Corti, Jul 01 2026

Status

approved