calculator sequence inspired by my calendar

[jos koot]

Hi,
Indeed, a practical test on all numbers below 1000000 has shown me that 15 does not occur as such a difference for these numbers. Of course there is a systematic way (a procedure, not an algorithm) of forming a sequence of all such differences. Things very much depend on the order in which you want form this sequence, I think. Furthermore I think the sequence has unlimited length, but that makes it all the more interesting. I guess you want a decision algorithm that given any number can decide whether or not it is the difference between a number and its upside down (more precisely rotated over 180 degrees) This is interesting, but I am not sure it is within my capacities. Nevertheless I intend to look into this problem, but this has to wait a week or so (Chrismas time you know)
Greetings, Jos Koot

----- Original Message ----- 
  From: Tanya Khovanova 
  To: seqfan at ext.jussieu.fr 
  Sent: Thursday, December 21, 2006 4:36 PM
  Subject: Re: calculator sequence inspired by my calendar


  I am looking for the numbers that can be represented as the difference of a number and its ipside down version on a calculator. I think I can prove that 15 is not there, but I do not have a systematic way to build this sequence.


  ---------- Original Message ----------------------------------
  From: "jos koot" <jos.koot at telefonica.net>
  Date:  Thu, 21 Dec 2006 00:27:15 +0100

  >Here are some solutions:
  >Greetings, Jos Koot
  >mabel 12, zane 21
  >mabel 15, zane 51
  >mabel 16, zane 91
  >mabel 18, zane 81

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