15/13
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| Ratio | 15/13 |
| Factorization | 3 × 5 × 13-1 |
| Monzo | [0 1 1 0 0 -1⟩ |
| Size in cents | 247.74105¢ |
| Name | tridecimal semifourth |
| Color name | 3uy2, thuyo 2nd |
| FJS name | [math]\text{A2}^{5}_{13}[/math] |
| Special properties | reduced |
| Tenney height (log2 nd) | 7.60733 |
| Weil height (log2 max(n, d)) | 7.81378 |
| Wilson height (sopfr (nd)) | 21 |
| Harmonic entropy (Shannon, [math]\sqrt{n\cdot d}[/math]) |
~4.55413 bits |
[sound info] | |
| open this interval in xen-calc | |
In 13-limit just intonation, 15/13, the tridecimal semifourth is an interval measuring about 247.7¢. In the language of Margo Schulter, 15/13 is an instance of an interseptimal interval, as it falls in an ambiguous zone between two septimal extremes – namely the large major second 8/7 and the small minor third 7/6. (15/13)×(13/10) = 3/2, which implies that 15/13 and 13/10 make a 3/2 perfect fifth. Thus you can make a root-3rd-P5 triad that goes 26:30:39, with a 15/13 inframinor third up from the root. When being used as type of second, it is given the name ultramajor second as it is even sharper than 8/7 which is often called a "supermajor second".