Sorry, no cool number days this week.

But, as promised on June 23, we will look at how much longer Half-back days are going to last this century.  Recall from the calculations back then, the way to find the DAY when the MONTH and YEAR are known is with the simple formula

                d = 2y – m   OR   d + m= 2y

There are limits on year, month, and day values:

                0 <= y <= 99  (only 100 years in a century!)

                1 <= m <= 12  (only 12 months in a year!)

                And day limits vary by month

                1 <= d <= 28 or 29 for February

                1 <= d <=30 for April, June, September, and November

                1 <= d <= 31 for January, March, May, July, August, October, and December

 

Start with January.

m = 1; d <=31; and d + m = 2y, so

31 + 1 <= d + m =2y

32 <= 2y

16 <= y

So, 1/31/16 (up 30 and back 15) is the last January half-back day of the century.

 

And look at February.

m = 2; d<=29; and d + 2m = 2y

29 + 2 <= d + m = 2y

31 <= 2y

15.5 <=y

Month and day have to both be even, for the 2y to work!

2/28/15 is the last February half-back day until 2/2/2100… wrap your head around that one!

 

We will figure out the rest of the months on October 6.  There will be a surprise because February’s 28 days masks a pattern.

We have some variety this week.

8/18/13 is the Half-back Day of the month.  8 to 18 is 10, and then 18 to 13 is half way back.

8/21/13 is a backwards subtraction day;  21-8 = 13.

AND, we have the last All Fibonacci numbers day, 8/21/13, until the year 2021.  Enjoy!

Tuesday, 8/13/13, is made up of all Fibonacci numbers  (See June 9 post, although you may be growing tired of it by now).

Monday, 8/5/13, does double duty for us this week:  8 + 5 = 13, so it is an Addition Day.  And, 8, 5, and 13 are all Fibonacci numbers  (See June 9 post).

8/8/13 is another All Fibonacci date.  Enjoy them while they last!

We leave July behind with TWO All Prime Days and we welcome August in with THREE All Fibonacci Days (See June 9 Post).

All Primes:  7/29/13 and 7/29/13

All Fibonacci:  8/1/13,  8/2/13, and 8/3/13

More All Fibonacci later this month, but no more All Primes until 11/2/13!

The big day this week is Tuesday, 7/23/13 – another All Prime day.

Right now, the odometer on my 2004 Honda Pilot is at 109,862.  So later today, when I am driving to the grocery and then to Jesse’s house, at some point it will read 10 9 8 7 6.

Thank you.

July is full of All Prime days.  Enjoy them while they last, because the next month with All Primes is November.  This week we have:  7/17/13 and 7/19/13.

7/19/13 is also the half-back day for the month.

And 7/20/13 is a nice Minus Subtract day: 20 – 7 = 13

Today is a rarity – 7/11/13 is made up of three CONSECTIVE prime numbers!  Tell that to the clerk at 7-Eleven when you ask for your free Slurpee.

Hobbits have much to commend them, including the celebration of half-birthdays – the date six months after (or before) your real birthday.  It turns out my half birthday is May 5.  AND, my 55^th half-birthday was 05-05-05!  I did not plan that.

Diane and I have our anniversary on September 9.  Our 27^th (3-cubed) anniversary was on 09-09-99 (all those 9s, each of which is 3-squared).  We also celebrated our 37^th anniversary on 09-09-09. The 37 does not quite fit the pattern, but it is a prime number – always worth looking for.  I did not plan that one either; it was Diane’s choice.

I also did not plan for open-heart surgery to have my aortic valve replaced on October 10, 2000.  The cardiologist said it should be done right away since he was worried about sudden death syndrome, and I was not into that at all. The result is that new valve turned 10 on 10-10-10.  The valve shared the date with Jacob DeYoung, who turned five that day.  I don’t think his parents planned that either, since his dad delivered him in the parking lot outside the hospital.

The one cool repeating number date event I did plan was the Elevens party on Friday, November 11, 2011.  My siblings and several friends arrived to watch the MSU Spartans play basketball on an aircraft carrier, take a wonderful quiz about fascinating facts of elevens, and try to stay awake until 11:11 PM. Sister Cindy had the unplanned part – her favorite team, the St Louis Cardinals, had just won the franchise’s eleventh World Series, having been 11 games behind earlier in the season and having won eleven playoff games on the way to the championship. She provided commemorative t-shirts.

Sorry, I got nothin’ for the other 8 repeat number dates this century, although I heard there were a record-setting number of weddings on Saturday, 07-07-07.