# [seqfan] Re: Pebble Transform and prime numbers

franktaw at netscape.net franktaw at netscape.net
Thu Nov 19 21:28:49 CET 2009

```I have several problems with this.

First (and least), "transform" is usually reserved for operations that
take one sequence into another (or other kinds of complexes, in other
contexts).  If you are just taking one number to another, just call it
a "function".

Second, this takes a nice (finite) sequence/partition transform, and
makes it an ugly, base-related numeric function.  (Consider for a
moment what happens to 1234567891.)

Third, the stopping conditions seem very arbitrary.  In particular,
primes are coming in from left field; there is nothing in the entire
subject that suggests that looking for primes is a relevant or
interesting thing to do.

-----Original Message-----
From: Eric Angelini <Eric.Angelini at kntv.be>

We could play the same game with the digits inside an integer...

Let's define the "Pebble Transform" (PT) like this:

--------------------------------------
Define 'd' as the number of non-zero digits (here d=4)
Make every digit minus 1, except for the zero digits (34102
--> 23001)
Write 'd' ahead of the result (423001)
--------------------------------------

... and now iterate the PT until:
- the resulting integer has more zeros at the end than the one which
was used for the first PT;
- the resulting integer is a prime

Best,
É.

```