A198587 Odd numbers producing 4 odd numbers in the Collatz iteration.

17, 35, 69, 75, 141, 151, 277, 301, 565, 605, 1109, 1137, 1205, 2261, 2275, 2417, 2421, 4437, 4549, 4821, 4835, 4849, 9045, 9101, 9669, 9685, 9699, 17749, 18197, 19285, 19341, 19397, 19417, 36181, 36405, 38677, 38741, 38797, 38833, 38835, 70997, 72789, 72817

Offset: 1

Author

T. D. Noe, Oct 31 2011

Keywords

• nonn

Comments

Start with A385110. If k is in sequence then so is 4*k + 1. - Ralf Stephan, Jun 18 2025

Links

• Vincenzo Librandi and T. D. Noe, Table of n, a(n) for n = 1..287 (first 134 terms from Vincenzo Librandi)

Crossrefs

Cf. A198584, A385110.

Programs

Mathematica

Collatz[n_] := NestWhileList[If[EvenQ[#], #/2, 3 # + 1] &, n, # > 1 &]; t = {}; Do[If[Length[Select[Collatz[n], OddQ]] == 4, AppendTo[t, n]], {n, 1, 100000, 2}]; t