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Vladimir Ladma
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Natural period

Definition

Let rational number qεQ has prime partition:
q = product(p(j)^a(j)), p(j)εP (primes), a(j)εZ (integers).

We call natural period r the expression:
r = product(p(j)).

Congruences

Number of classes of expression
n^k mod k , n,kεNo (zero and positive integers),
is equal to natural period r of number k.

n\k 1 2 3 4 5 6 7 8 9101112
 0  0 0 0 0 0 0 0 0 0 0 0 0
 1  0 1 1 1 1 1 1 1 1 1 1 1
 2  0 0 2 0 2 4 2 0 8 4 2 4
 3  0 1 0 1 3 3 3 1 0 9 3 9
 4  0 0 1 0 4 4 4 0 1 6 4 4
 5  0 1 2 1 0 1 5 1 8 5 5 1
 6  0 0 0 0 1 0 6 0 0 6 6 0
 7  0 1 1 1 2 1 0 1 1 9 7 1
 8  0 0 2 0 3 4 1 0 8 4 8 9
 9  0 1 0 1 4 3 2 1 0 1 9 9
10  0 0 1 0 0 4 3 0 1 0 10 4
11  0 1 2 1 1 1 4 1 8 1 0 1
12  0 0 0 0 2 0 5 0 0 4 1 0

Dissonance amount

Let us have two tones, whose frequency ratio f1/f2 can be approximated by fraction q.
We assume, dissonance amount of this chord depends on natural period r (computed from prime partition of q).
A special case of this phenomenon is octave identity.

Consonance of ratio 2:1 (octave) is assumed to be the same as consonance of 4:1 (two octaves); similarly ratio 3:2 (fifth) is perceived like as 4:3 (fourth).
Prime 2 has special meaning in music: ratio 2:1 is also considered to be the same as ratio 1:1.