Adjacent ratio is a ratio between the frequency of the 2 successive Shrutis.
I worked out the 'Adjacent ratios' between all 22 shrutis and they showed a definite repetitive pattern or a unique formula, with age-old mathematical numbers governing the ratios such as the Pythagoran Limma, and Syntonic Comma.

Figure shows the definite repetitive pattern of ratios between adjacent shrutis.
Let us take Shadja as that of the middle C in the keyboard, with the ET frequency of 261.6255528 Hz (Obtained by dividing 440 by 1.0594631, by 9 times).
Shrutis are based on 3 Successive or Adjacent Ratios as shown below. (Refer to following tables)

Table shows 3 Principle Adjacent ratios for 22 Shrutis

Table shows the working of the Code of Adjacent ratios
Thus the cycle of the chain of adjacent ratios:
The sequence is not haphazard, but has a peculiar design !The values of 1, 2, and 3 are those of the Adjacent Ratios 1, 2, and 3 respectively as given above.