Besides $3x - 1$, $5x + 1$, which variants of the $3x + 1$ problem have been proven conclusively one way or the other? [duplicate]
Months ago, I asked In the $x + 1$ problem, does every positive integer $x$ eventually reach $1$? I think it's fairly easy to adapt the arguments given in the answers to that one to prove that $x - 1$ always reaches $1$ as well.
It's also well known that $3x - 1$, $5x - 1$ and $5x + 1$ all have readily found cycles that don't include $1$. I think I also found cycles for $7x + 1$ but I seem to have misplaced the relevant notebook.
My question today is: which other variants of $3x + 1$ have been studied and proven to always or not always reach $1$? And is there a paper or a book that gathers a lot of the available research on the variants?
Write
$$ b = { m \cdot a + 1 \over 2^A} $$ for one transformation with odd multiplicator $m$ and odd $a \to b$.
Then there is for all $m=2^M-1$ the trivial cycle $1 \to 1$ and for all $m=2^M+1$ the trivial cycle $-1 \to -1$
Besides the cycles you refer to, in the literature it is also known the cycle with $m=181$ on $a=27$, $b=611$ (I think) and I found a second one on $a=35$.
I didn't find any more cycle - either numerically with tests up to $m$ some thousands and projected cycle lengthes up to some 100. Also I didn't find something more in literature. (Btw. shouldn't this all be in a section in wikipedia's Collatz-article under "generalization"? Curious - I'll see later, I'm just in a holiday)
Note, that allowing negative $m$ we find two more $m$ allowing small cycles, but have it not at hand, see some of my recent questions/answers concerning the collatz-problem.
Update Inspired by the finding in an arxiv-article linked by some recent Q&A about cycles in a $7x \pm 1$ - problem, defined by $$ f(n) = \left \lbrace \begin{matrix} n/2 & \text{if $n$ is even} \\ 7n +1& \text{if } n \equiv 1 \pmod 4) \\ 7n -1& \text{if } n \equiv 3 \pmod 4) \\ \end{matrix}\right.$$
$ \qquad $which can also be rewritten as $ b = { 7 \cdot a + (2 - a \% 4) \over 2^A} $ for one transformation where the $\%$-sign denotes the residue function with modulo $4$ (often called
mod
in programming languages) I looked at the obvious generalizations with $m=\{3,5,7,9,11,13,15,17,19\}$ (of course with the meaningful adaption of the $a \% 4$-rule) and found the following cycles testing small numbers:
m cycles, (?likely) divergences
----+------------------------------------------
3 1,1,...
5 1,1,...
7,9,11,7,...
7 1,1,...
9 1,1,...
13, 29, 65, 73, 41, 23, 13, ...
(? divergences...)
11 1,3,1,...
(?divergences)
13 1,3,5,1,...
25, 81, 263, 855, 2779, 1129, 3669, 2981, 1211, 123, 25, ...
49, 159, 517, 105, 341, 277, 225, 731, 297, 965, 49 ,...
(?divergences)
15 1,1,...
(?divergences)
17 1,1,...
(?divergences)
19 (?divergences)
181 27,611,27,...
35,99,35, ...
(?divergences)
All found cycles have exact counterparts in the negative numbers.