π Stoas near [[2023 09 29]]
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π 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.
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