📕 subnode [[@flancian/2023 09 29]]
in 📚 node [[2023-09-29]]
- [[29]] is [[drishti]] in the #Flancia [[Pattern Language]].
-
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 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 because 22 is.
- 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.
-
I find this one quite beautiful, this is how I got there:
-
[[1547]] is not prime; it is 7 * 13 * 17.
- I got to this one by whistling a 1547 tone, seeing it in [[spectroid]], then checking https://anagora.org/prime/1547 :)
-
Take [[209]] -- it is not prime.
📖 stoas
- public document at doc.anagora.org/2023-09-29
- video call at meet.jit.si/2023-09-29