flancian/garden
0
0
Fork 0
mirror of https://github.com/flancian/garden.git synced 2026-08-07 23:16:21 +00:00
Code Issues Packages Projects Releases Wiki Activity

autopushed

Browse Source
This commit is contained in:
Flancian
2023-09-29 00:58:55 +02:00
parent 960f244391
commit e1c1973e47
1 changed files with 13 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files
journal/2023-09-29.md
+13 -4
View File
@@ -1,8 +1,17 @@
- [[29]] is [[drishti]] in the #Flancia [[Pattern Language]].
- My hobby: think about whether numbers are prime.
- [[209]] is not prime; it is 19 * 11.
- I find this one quite beautiful as there are two simple "proofs" to get there:
- My hobby, sometimes: think about whether numbers are prime while laying down or sitting.
- Take [[209]] -- it is not prime.
- I find this one quite beautiful, this is how I got there:
- It is not multiple of two or five trivially.
- It is not a multiple of three as its digits don't add up to a multiple.
- It is not a multiple of 7 as 210 is (as 21 is 3 * 7); and it's too near to it.
- It is not a multiple of 7 because 210 is (as 21 is 3 * 7) and it's too near.
- Consider the hypothesis that it is multiple of 11.
- 220 is a multiple of 11.
- 220 - 11 is 209.
- So 209 is a multiple of 11. What is the other factor?
- Consider the hypothesis that it is a multiple of 19.
- 19 * 10 is 190.
- 190 + 19 is 209 precisely, so it is a multiple.
- Therefore 209 is 11 * 19.
- [[1547]] is not prime; it is 13 * 7 * 17.
- I don't remember how I got here but it was fun.