The Kitchen Sink and Other Oddities

Atabey Kaygun

Collatz-type Conjectures (Continued)

After the last two posts, I think I need to explain the reason why I chose the functions\[f_p(n) =\begin{cases}f_p(n/p) & \text{ if $p$ divides $n$ }\\n & \text{otherwise}\end{cases} \] and \[ g_p(n) = \begin{cases} g_p( f_p (n) ) & \text{ if $p$ divides $n$ }\\ f_p( np + n + p - (n \text{ mod } p) ) & \text{ otherwise } \end{cases} \] as the proper generalization of the function \(3n+1\) of the Collatz Conjecture. For that we need to go back to the original conjecture.

A look at the original conjecture in the binary

Consider the functions in the original conjecture in the binary. We have two functions \[ f(n) = \begin{cases} n/2 & \text{ if $n$ is even }\\ n & \text{otherwise} \end{cases} \] and \[ g(n) = \begin{cases} f(n) & \text{ if $n$ is even }\\ f(3n+1) & \text{ otherwise} \end{cases} \] The first function deletes one trailing 0 in the binary description of \(n\) while the other does

  1. Takes \(n\) and shifts it to left by one digit.
  2. Adds the original \(n\) to the result.
  3. Adds one to the result.

For example: if \(n\) were \(10001\) in binary then \[ 100010 + 10001 + 1 = 110011 + 1 = 1100100 \] And after deleting the trailing 0’s we get \(11001\). The cycle we would like our all recursive sequences to end with is \[ 1 \rightarrow 11 + 1 = 100 \rightarrow 10 \rightarrow 1 \] I don’t know you but this behaves like a 1-D version of a Conway’s Game of Life, or more generally, a Cellular Automaton.

So, I thought wouldn’t it be neat if one defined a similar game for representations of natural numbers in base \(p\). Hence I defined \(f_p(n)\) and \(g_p(n)\).