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Old 2019-02-16, 18:10   #1
neskis's Avatar
Feb 2019

100002 Posts
Default Primality based on digital root


Has anyone besides me noticed this?

Primes are the sum of two CONSECUTIVE integers ONLY as follows:

Prime DR1 = integer DR0 + integer DR1
Prime DR2 = integer DR5 + integer DR6
Prime DR4 = integer DR6 + integer DR7
Prime DR5 = integer DR2 + integer DR3
Prime DR7 = integer DR3 + integer DR4
Prime DR8 = integer DR8 + integer DR0
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Old 2019-02-16, 20:01   #2
Batalov's Avatar
Mar 2008

23·5·229 Posts

Yeah. And it has nothing to do with "primes". Primes in your message is a red herring.

This is called modular arithmetic. Look it up.

DR is nothing else than mod(9).
What you are doing is: using mod(9) you are trying to solve:
x + (x+1) = a (mod 9).
But the solution is obvious:
x = (a-1)/2 (mod 9)

you are saying: "DR4 = integer DR6 + integer DR7".
Or in other words: "4 = 6+7 (mod 9)".
That's obvious, because 6 = (4-1)/2 (mod 9).

(look up how to divide by 2 in a modular system)
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