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Palindromic Date

Dod101
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Palindromic Date

#178970

Postby Dod101 » November 8th, 2018, 11:52 am

I have just noticed that today is one of those relatively unusual dates which is not only palindromic but it also reads the same upside down 8.11.18 (at least as palidromic as any date ever is).

Dod

UncleEbenezer
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Re: Palindromic Date

#178976

Postby UncleEbenezer » November 8th, 2018, 12:35 pm

We have equally "palindromic" dates three months running just now. Among others.

Gengulphus
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Re: Palindromic Date

#179004

Postby Gengulphus » November 8th, 2018, 3:24 pm

We've had 8.1.18 and 8.10.18 this year as well as 8.11.18 today, all with the same palindromic and reflective properties as today - and I don't believe we get another one until 8.8.88. So make the most of it while it lasts! ;-)

Gengulphus

Dod101
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Re: Palindromic Date

#179006

Postby Dod101 » November 8th, 2018, 3:36 pm

Gengulphus wrote:We've had 8.1.18 and 8.10.18 this year as well as 8.11.18 today, all with the same palindromic and reflective properties as today - and I don't believe we get another one until 8.8.88. So make the most of it while it lasts! ;-)


I can fairly confidently say that I will not be around for 8.8.88 but the Cantonese will love that. Will be making plans already!

Dod

UncleEbenezer
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Re: Palindromic Date

#179007

Postby UncleEbenezer » November 8th, 2018, 3:39 pm

Gengulphus wrote:We've had 8.1.18 and 8.10.18 this year as well as 8.11.18 today, all with the same palindromic and reflective properties as today - and I don't believe we get another one until 8.8.88. So make the most of it while it lasts! ;-)

Gengulphus

Nonsense. Just treat your digit 2 as a matchstick puzzle, and it rotates nicely for all those 02..20, 12..21 dates, as well as lots of four- and five-digit dates through the next decade.

Gengulphus
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Re: Palindromic Date

#179014

Postby Gengulphus » November 8th, 2018, 3:57 pm

UncleEbenezer wrote:
Gengulphus wrote:We've had 8.1.18 and 8.10.18 this year as well as 8.11.18 today, all with the same palindromic and reflective properties as today - and I don't believe we get another one until 8.8.88. So make the most of it while it lasts! ;-)

Nonsense. Just treat your digit 2 as a matchstick puzzle, and it rotates nicely for all those 02..20, 12..21 dates, as well as lots of four- and five-digit dates through the next decade.

The only nonsense is that you're talking about rotations when I said "reflective". By all means come up with your own list of interesting dates, but don't try to make out that I'm talking about it when I'm not.

Gengulphus

gryffron
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Re: Palindromic Date

#179026

Postby gryffron » November 8th, 2018, 4:42 pm

Gengulphus wrote: I don't believe we get another one until 8.8.88. So make the most of it while it lasts! ;)


1.8.81 ??

UncleEbenezer
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Re: Palindromic Date

#179029

Postby UncleEbenezer » November 8th, 2018, 4:59 pm

gryffron wrote:
Gengulphus wrote: I don't believe we get another one until 8.8.88. So make the most of it while it lasts! ;)


1.8.81 ??

18.1.81 in that year, without offending Gengulphus' rules.

Though if we make it really invariant under reflection, it looks somehow different: |8:|:8|

[aside] Your reference to '81 screamed of turning the clock back, in a way '88 never did. Funny how some times in one's life stick much more than others. Or perhaps it was knowing Gengulphus to be a Cambridge man that brought the association of a year when I was a student there.

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Re: Palindromic Date

#179038

Postby Howard » November 8th, 2018, 5:36 pm

12.1.21 ?

Dod101
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Re: Palindromic Date

#179048

Postby Dod101 » November 8th, 2018, 6:00 pm

Howard wrote:12.1.21 ?


That would be a palindrome but it is not reflective in the way that say today's date is. As we can see there are a lot of palindromic dates but far fewer reflective ones (in the sense that we are writing about anyway)

Dod

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Re: Palindromic Date

#179099

Postby Gengulphus » November 9th, 2018, 7:47 am

UncleEbenezer wrote:
gryffron wrote:
Gengulphus wrote: I don't believe we get another one until 8.8.88. So make the most of it while it lasts! ;)

1.8.81 ??

18.1.81 in that year...

Good points - yes, I overlooked those.

UncleEbenezer wrote:Though if we make it really invariant under reflection, it looks somehow different: |8:|:8|

Well, yes - all of these, including the ones in the OP, are liable to become invalid when you look at the details of the font - and which ones become invalid depends on exactly which font is being used. On my screen, for instance, yesterday wasn't unchanged when turned upside down, because of the serif on the '1', the top loop of the '8' being slightly smaller than the bottom loop, and the '8' not even being quite invariant under left-right reflection, though that's hard to see unless one zooms in a lot... So basically, right from the start of the thread, I took it that there was an assumption that a suitably-symmetric font is being used.

Gengulphus

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Re: Palindromic Date

#179102

Postby Gengulphus » November 9th, 2018, 7:58 am

Dod101 wrote:
Howard wrote:12.1.21 ?

That would be a palindrome but it is not reflective in the way that say today's date is. As we can see there are a lot of palindromic dates but far fewer reflective ones (in the sense that we are writing about anyway)

There's a bit of an ambiguity there with regard to what your OP says - "upside down" could either mean "unchanged when rotated 180 degrees" or "unchanged when reflected top-bottom". Using a 'matchstick' font, 12.1.21 meets the first of those and not the second - and in addition, Howard didn't make it clear whether he was suggesting 12.1.21 as a reply to your OP or to my reply...

Gengulphus

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Re: Palindromic Date

#179164

Postby Howard » November 9th, 2018, 12:11 pm

Gengulphus wrote:
Dod101 wrote:
Howard wrote:12.1.21 ?

That would be a palindrome but it is not reflective in the way that say today's date is. As we can see there are a lot of palindromic dates but far fewer reflective ones (in the sense that we are writing about anyway)

There's a bit of an ambiguity there with regard to what your OP says - "upside down" could either mean "unchanged when rotated 180 degrees" or "unchanged when reflected top-bottom". Using a 'matchstick' font, 12.1.21 meets the first of those and not the second - and in addition, Howard didn't make it clear whether he was suggesting 12.1.21 as a reply to your OP or to my reply...

Gengulphus


The honest answer is that I didn't fully understand your Palindrome rules!

I could be devious and suggest that my chosen font is an unusual one which my grandchildren sometimes slip into and write their "2" like a back to front "S", but that would be an attempt to justify my rather too hasty suggestion.

Please consider my suggestion humbly withdrawn. :)

regards

Howard


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