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A prime date
Posted: Mon Jan 03, 2011 6:15 pm
by owlice
103 is a prime number, as is 2011. So today's a prime date.
That is all.
Re: A prime date
Posted: Mon Jan 03, 2011 6:38 pm
by neufer
owlice wrote:
103 is a prime number, as is 2011. So today's a prime date.
Not quite sure why 1/3/2011 or 1032011 (= 41 x 25171)
[or 3012011 (= 23 x 130957)] aren't more relevant.
1/3/2011 (or 3/1/2011) could be said to be prime however.
As was 11/29/2003 (or 29/11/2003).
However, the next prime Julian day is 2455577 = 2011-01-15 12:00:00 UTC
http://www.fourmilab.ch/yoursky/help/controls.html#Julian wrote:
<<Astronomers often have to do arithmetic with dates and times. The Gregorian calendar is sufficiently eccentric that answering a question like “What is the date and time 295.03589 days (10 lunar months) from now?” is a nontrivial exercise. To facilitate computation, astronomers employ the Julian day calendar. The Julian day number for a given moment in time is simply the number of days, whole and fractional, elapsed since noon (12:00) Universal time on 1st January −4712; time is expressed as a fraction of a day. This system allows assigning a positive number to the date and time of any observation in recorded history and arbitrarily far into the future, and permits ordinary arithmetic with dates and times without having to worry about B.C. and A.D., Julian and Gregorian calendars, leap years, and all that. Of course, you need to be able to convert back and forth between Julian days and the civil calendar, but that's what computers are for.>>
Re: A prime date
Posted: Mon Jan 03, 2011 6:45 pm
by owlice
As was 01/01/2011, and is this Friday, and...
Perhaps the others are more relevant; it just occurred to me both the year and the date were prime, is all. I had noticed that the current number of members (4943) was a prime number, and that's what got me thinking about it.
Re: A prime date
Posted: Mon Jan 03, 2011 6:55 pm
by neufer
owlice wrote:
As was 01/01/2011, and is this Friday, and...
http://en.wikipedia.org/wiki/Prime_number wrote:
<<
A natural number is called a prime or a prime number if it has exactly two distinct natural number divisors. Natural numbers greater than 1 that are not prime are called composite.
Therefore, 1 is not prime, since it has only one divisor, namely 1. However, 2 and 3 are prime, since they have exactly two divisors, namely 1 and 2, and 1 and 3, respectively. Next, 4, is composite, since it has 3 divisors: 1, 2, and 4.
A prime number (or a prime) is a natural number that has exactly two distinct natural number divisors: 1 and itself. The smallest twenty-five prime numbers (all the prime numbers under 100) are: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97.>>
Re: A prime date
Posted: Mon Jan 03, 2011 7:14 pm
by owlice
Oh, neufer, that list of primes under 100 just reminded me of something... I've mentioned before that my son has an autistic spectrum disorder. When he was little, he would sometimes get lost in his emotions and spiral down into... oh, hard to know what to call it. Just a bad place. Once he started to spiral down, it was hard to stop his descent. He was 6, maybe 7, and attending a special ed school. One day, he started to fall apart. Fortunately, the social worker who was with him at the time not only understood my kid, but was creative and quick on her feet; to try to stop the spiral down, she said, "[Name!] Count backwards from 100 by prime numbers!" And that was it -- the crisis was averted; he was immediately and wholly engaged in the task.
I would never have thought of having him do that!
Re: A prime date
Posted: Mon Jan 03, 2011 7:42 pm
by BMAONE23
here is an interesting chart I made of Primes between 1 & 100(8) the last prime is 997 All the white squares are primes
Re: A prime date
Posted: Mon Jan 03, 2011 7:51 pm
by owlice
BMAONE23, thanks for sharing that! It's very cool!
: wonders how well the pattern of colors would translate to a scarf or quilt :
Re: A prime date
Posted: Mon Jan 03, 2011 9:40 pm
by neufer
owlice wrote:
"[Name!] Count backwards from 100 by prime numbers!" And that was it -
- the crisis was averted; he was immediately and wholly engaged in the task.
I would never have thought of having him do that!
Did he stop at 2?
Perhaps your son would be interested in one of the free (and completely safe)
program downloads at Dmitry Brant's website:
http://dmitrybrant.com/2007/01/05/primespiral
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1/3/2011 (or 3/1/2011) could still be said to be prime
since it is the 3rd day of 2011.
The last such day was the 359th day of 2003 (Xmas of 2003).
The first day with a prime month, day & year will be 2/3/2011
The first day with a prime day, month & year and day of the year
will be 3/7/2011 (the 67th day of the year).
Re: A prime date
Posted: Mon Jan 03, 2011 10:48 pm
by owlice
neufer wrote:Did he stop at 2?
I don't know; I wasn't there, as he was at school, and I never thought to ask how far he got!
I will let him know about that site; thanks!
He has told me he is not going to take any more math classes.
I wish he'd take one more semester of calculus, but it seems that might not happen.
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neufer wrote:1/3/2011 (or 3/1/2011) could still be said to be prime
since it is the 3rd day of 2011.
The last such day was the 359th day of 2003 (Xmas of 2003).
The first day with a prime month, day & year will be 2/3/2011
The first day with a prime day, month & year and day of the year
will be 3/7/2011 (the 67th day of the year).
Do we now start a discussion on whether 1 is prime?
Re: A prime date
Posted: Mon Jan 03, 2011 11:10 pm
by bystander
owlice wrote:Do we now start a discussion on whether 1 is prime?
Wikipedia wrote:Primality of one
One of the primary reasons to exclude 1 from the set of prime numbers is the
fundamental theorem of arithmetic, which says that every positive integer
x can be uniquely written as a product of primes. When
x is itself prime, this factorization has only one prime (
x itself) in it, and when
x = 1 the factorization is the
empty product. But if 1 were admitted as a prime, then any integer could be factored in an infinite number of ways. For example, in this case the number 3 could be factored as 1
k · 3 = 3 for any integer
k.
More generally, in
unique factorization domains, every non-zero element is a unique product of
prime elements and a
unit. The factorization would not be unique if products of units were allowed.
Re: A prime date
Posted: Mon Jan 03, 2011 11:23 pm
by owlice
Hey, I'm not the one (heh) trying to use 1 as a prime number; you need to aim that Wikipedia at neufer!
Re: A prime date
Posted: Mon Jan 03, 2011 11:51 pm
by bystander
neufer wrote:The first day with a prime day, month & year and day of the year
will be 3/7/2011 (the 67th day of the year).
March 7th is the 66th day of the year.
Re: A prime date
Posted: Mon Jan 03, 2011 11:58 pm
by neufer
bystander wrote:neufer wrote:The first day with a prime day, month & year and day of the year
will be 3/7/2011 (the 67th day of the year).
March 7th is the 66th day of the year.
My bad. So what is the answer?
Re: A prime date
Posted: Tue Jan 04, 2011 12:10 am
by bystander
neufer wrote:My bad. So what is the answer?
05/07/2011 - 127
05/11/2011 - 131
05/17/2011 - 137
05/19/2011 - 139
05/29/2011 - 149
05/31/2011 - 151
Re: A prime date
Posted: Tue Jan 04, 2011 12:11 am
by owlice
neufer wrote:So what is the answer?
42, of course.
Re: A prime date
Posted: Tue Jan 04, 2011 12:12 am
by Beyond
owlice wrote: Do we now start a discussion on whether 1 is prime?
That depends -- Are you ribs, steak or roast??
Re: A prime date
Posted: Tue Jan 04, 2011 12:20 am
by bystander
owlice wrote:neufer wrote:So what is the answer?
42, of course.
42 isn't prime, though.
Re: A prime date
Posted: Tue Jan 04, 2011 12:42 am
by owlice
I know that, but it's still the answer!
Re: A prime date
Posted: Tue Jan 04, 2011 4:27 am
by neufer
bystander wrote:neufer wrote:
So what is the answer?
05/07/2011 - 127
05/11/2011 - 131
05/17/2011 - 137
05/19/2011 - 139
05/29/2011 - 149
05/31/2011 - 151
05/17/2011 - 137 = Julian day starting at noon: 2,455,699 (Prime)
Re: A prime date
Posted: Tue Jan 04, 2011 8:26 am
by bystander
neufer wrote:05/17/2011 - 137 = Julian day starting at noon: 2,455,699 (Prime)
Now, that is a prime date. Need something special for that.
Thank goodness there is plenty of time to find a prime date for this.
Re: A prime date
Posted: Tue Jan 04, 2011 1:40 pm
by Beyond
neufer wrote:Therefore, 1 is not prime, since it has only one divisor, namely 1.
That's why Three Dog Night sang that 1 is the loneliest number. It has no one but itself to go out on a date with.
Re: A prime date
Posted: Mon Jan 10, 2011 3:38 am
by owlice
Not a prime date, but an interesting set of numbers:
Total posts 67829 • Total topics 6116 • Total members 5000
Re: A prime date
Posted: Mon Jan 10, 2011 4:22 am
by Beyond
Total members 5000
Where are they
Re: A prime date
Posted: Mon Jan 10, 2011 4:56 am
by owlice
Most of them are on their way to your house for the week; hope you went grocery shopping today!
Re: A prime date
Posted: Mon Jan 10, 2011 2:38 pm
by Beyond
Tell them to bring their shovels. I haven't yet cleared the walkway in front of my house, or the back porch, in case they try to sneak in
