18/13

Interval information

Ratio	18/13
Factorization	2 × 32 × 13-1
Monzo	[1 2 0 0 0 -1⟩
Size in cents	563.3823¢
Names	tridecimal augmented fourth, low tritone
Color name	3u4, thu 4th
FJS name	[math]\displaystyle{ \text{A4}_{13} }[/math]
Special properties	reduced
Tenney height (log2 nd)	7.87036
Weil height (log2 max(n, d))	8.33985
Wilson height (sopfr(nd))	21
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In 13-limit just intonation, 18/13, the tridecimal augmented fourth is a low tritone measuring about 563.4¢. It represents the interval between the 13th and 18th harmonics of the harmonic series.

The low tritone in 17edo approximates 18/13 quite well, while 17edo's approximations of 13/8 and 9/8 are both a little sharp. The inversion of 18/13 is 13/9, a high tritone measuring about 636.6¢; the interval between these two tridecimal (13-based) tritones is 169/162, approximately 73.2¢.

See also

• 13/9 – its octave complement
• 13/12 – its fifth complement
• Gallery of just intervals