## dinsdag 15 augustus 2017

### Pythagoras day

Today, 15 August '17 is a Pythagoras day, where day, month and year obey the Pythagorean Theorem: a^2 + b^2 = c^2. (^2 is the nerd notation of squared, because I cannot find the superscript).
Let's do the math:
15 x 15 = 225
8 x 8 = 64 (in case you are puzzled: this is August)
17 x 17 = 289
225 + 64 = 289

Each century has 28 Pythagoras days. You find a complete list below, but first some explanation.
My definition of Pythagoras day is a bit wider than on other sites. On this site you can read: Pythagorean Theorem Day or Pythagoras Theorem Day is celebrated when the sum of the squares of the first two digits in a date equals the square of the last digit in the date. The last number is the year.
In my list also day and month can be the largest number. By the way: today is Pythagoras day according to all definitions.

The stricter definition can have 2 Pythagoras days per Pythagorean triplet, while my definition gives a maximum of 6 dates. Notice that the first 6 Pythagorean days all go back to the triplet 3,4,5. The stricter definition will only accept numbers 5 and 6.

Not all Pythagorean triplets have 6 dates. E.g. 5,12,13 has only 4, because 13 cannot be used as month.
The fact that there are only 28 Pythagoras days is mainly due to the fact that we have just 12 months and rapidly increasing a, b and c.
However there are some combinations that cannot be used, because there are maximum 31 days in a month. Else these would have had 40 September '41 and 60 November '61.

Enjoy the list and see you again on 16 December '20.

1) 5 April '03
2) 4 May '03
3) 5 March '04
4) 3 May '04
5) 4 March '05
6) 3 April '05
7) 13 December '05
8) 10 August '06
9) 8 October '06
10) 10 June '08
11) 6 October '08
12) 15 December '09
13) 8 June '10
14) 6 August '10
15) 13 May '12
16) 15 September '12
17) 12 May '13
18) 5 December '13
19) 17 August '15
20) 12 September '15
21) 9 December '15
22) 20 December '16
23) 15 August '17
24) 16 December '20
25) 25 July '24
26) 26 October '24
27) 24 July '25
28) 24 October '26