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<DIV>Hi,</DIV>
<DIV>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)</DIV>
<DIV>Greetings, Jos Koot</DIV>
<DIV> </DIV>
<DIV>----- Original Message ----- </DIV>
<BLOCKQUOTE
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=tanyakh@TanyaKhovanova.com
href="mailto:tanyakh@TanyaKhovanova.com">Tanya Khovanova</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=seqfan@ext.jussieu.fr
href="mailto:seqfan@ext.jussieu.fr">seqfan@ext.jussieu.fr</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Thursday, December 21, 2006 4:36
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: calculator sequence inspired
by my calendar</DIV>
<DIV><BR></DIV>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.<BR><BR><BR>---------- Original Message
----------------------------------<BR>From: "jos koot" <<A
href="mailto:jos.koot@telefonica.net">jos.koot@telefonica.net</A>><BR>Date:
Thu, 21 Dec 2006 00:27:15 +0100<BR><BR>>Here are some
solutions:<BR>>Greetings, Jos Koot<BR>>mabel 12, zane 21<BR>>mabel
15, zane 51<BR>>mabel 16, zane 91<BR>>mabel 18, zane
81<BR><BR></BLOCKQUOTE></BODY></HTML>