21/13

21/13, the tridecimal supraminor sixth, is ca. 830 cents in size. It has a very good approximation in 13edo.

Interval information

Ratio	21/13
Factorization	3 × 7 × 13-1
Monzo	[0 1 0 1 0 -1⟩
Size in cents	830.2532¢
Name	tridecimal supraminor sixth
Color name	thuzo 6th, 3uz6
FJS name	[math]\displaystyle{ \text{M6}^{7}_{13} }[/math]
Special properties	reduced
Tenney norm (log2 nd)	8.09276
Weil norm (log2 max(n, d))	8.78463
Wilson norm (sopfr(nd))	23
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This interval is a ratio of two consecutive Fibonacci numbers, therefore it approximates the golden ratio. In this case, 21/13 is ~2.8 ¢ flat of the golden ratio.

See also

• 26/21 – its octave complement
• Gallery of just intervals