This is a great week for cool number days.

Three All Prime days:  7/7/13, 7/11/13, 7/13/13.

And the middle one is three CONSECTIVE prime numbers!  The last one of those was 5/7/11, and the next one is the last one this century: 11/13/17.

Bonus this week – Wednesday, 7/10/13 is an additive sequence.

Delicious opportunity this week on the consecutive primes day – Free Slurpees on 7/11 at 7/11.

 

After having no cool days last week (and having to punt with a math lesson), it is great to hit a PRIME number stretch.

Three days this week, 7/2/13, 7/3/13, and 7/5/13 are all prime numbers!

Bonus – Saturday 7/6/13 is additive: 7 + 6 = 13

 

This week has no cool number dates. 

But we can use the time to explain how to determine which day of the month will be a half-back day. 

Recall that Half-back days are named in honor of all the retirees who move from Northern states (Michigan, Minnesota, New York, etc) to Florida, find out Florida is too hot, and then move to middle ground in Tennessee or North Carolina or around there someplace.

So, start at the month, go to the day, and come half way back to the year.

If the integers for month / day / year are m/d/y, then the problem is to solve for d when m and y are  known.  The one equation we need is:

                d – y = (d – m)/2

                2( d – y ) = d – m

                2d – 2y  = d – m

                d = 2y – m

For next month, m is 7 and y is 13, so the half-back day is 26 – 7 = 19.  Since each succeeding month value for the rest of the year increases by 1, the half-back d decreases by 1:

                8/18/13

                9/17/13

                10/16/13

                11/15/13

                12/14/13

For the next week with no cool number days (8/25/13), we will examine when the half-back days will end this century.

 

Wednesday this week (6/19/13) is a Minus Subtract Day:  19 minus 6 equals 13.

Thursday (6/20/13) is this month’s Half-back Day:  Move up 14 from 6, then come half way (7) back to 13.  See the May 19^th post for the definition and history of half-back days.  Tune in next Sunday for instructions on how to calculate the day of the month that will act like a half-back.

No cool number days this week. 

But, I just realized there is a whole set of numbers out there I have overlooked – the Fibonacci sequence.  It is easy but elegant.  Start with 0 and 1.  Add them together.  Always add the latest two numbers together to get the next one.  The first 10 numbers in the sequence are:

        0 , 1, 1, 2, 3, 5, 8, 13, 21, 34

(see that 0+1=1; 1+1=2; 1+2=3; 2+3=5…)

Quiz: what is the next number?

For our cool number dates, I am sorry I missed 05/08/13.  Just a month ago, there were three sequential Fibonacci numbers!  Pretty rare… next one is not until 2021, and that is the last one of this century!

 Fortunately, in August there will be some month/day/year combinations that are all Fibonacci, just not presented sequentially. They start with 08/01/13 and end with 08/21/13.  To see how many others there are, check back here on the Sundays from July 28 through August 18. 

Look for a wonderful reference to Fibonacci numbers in the movie “Mr. Magorium’s Wonder Emporium.”

 

 

 

Quiz Answer: 55

Friday this week is an Addition Day:  06 + 07 = 13.

Every month this century has had one Addition Day where the Month + Day = Year.  (This uses the definition that the first year of the century was 2001, since there was no year zero).  Addition days will stop at some point.  We will name that point in a later post.  Don’t worry, it won’t happen for a while!

I like to think of Thursday, 6/6, as Gravity Day. The gravitational constant G ~  6.672 x 10^11.  I made up Gravity Day.  Fortunately for all of us, I did not have to make up G; it was already there.

Sunday, May 26

>June sneaks in at the end of the week!  June was packed with cool dates last year because 6 and 12 fit together nicely.  But, this year is sparse because 6 and 13 do not play well together.

>For the third week in a row, there are two All Prime days:  05/29/13 and 05/31/13.

If we say “at least” two All Prime days, then this is the fifth week in a row, since the week beginning 05/05/13 (el Cinco de Mayo) had THREE All Prime Days.

Sorry, no more All Prime days until July.

With a title like Los Tres, this has to be about numbers, right? It is, but maybe not what you think.

Last night at Los Tres Amigos, we ordered two fountain drinks, a taco salad, and a chimichanga.  The total bill was 22.22

Go to Lou and Harry’s and order a regular Greek Chicken salad and a hamburger combo.  The cost will be 16.17, which is cool.  But then you add a nice take-out tip of $1 to make the total 17.17.  Two fun amounts on one bill.

 

You can go order the same things and check it out, at least until the menu or prices change!

Sunday, May 19 

>Once again, there are two All Prime days, where the month, day, and year are all prime numbers: 05/19/13 and 05/23/13.

 

>05/21/13 is a half-back day.  Start at the month and go to the day, then come half-way back to the year.  5 to 21 is 16, and 21 back to 13 is 8.

Half-back days are named in honor of all the retirees who move from Northern states (Michigan, Minnesota, New York, etc) to Florida, find out Florida is too hot, and then move to middle ground in Tennessee or North Carolina or around there someplace.

Every month this year (and for the near future) has one half-back day. Another post is coming that will explain how to calculate the day, given the month and year.