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Interval information
Ratio 81/40
Factorization 2-3 × 34 × 5-1
Monzo [-3 4 -1
Size in cents 1221.5063¢
Name syntonic octave
Color name g8, gu octave
FJS name [math]\text{P8}_{5}[/math]
Tenney height (log2 nd) 11.6618
Weil height (log2 max(n, d)) 12.6797
Wilson height (sopfr (nd)) 23
Harmonic entropy
(Shannon, [math]\sqrt{nd}[/math])
~4.11673 bits
open this interval in xen-calc

The ratio of 81/40 is the distance between the 81st and 40th harmonic, which can be seen as an octave that is augmented by a syntonic comma (81/80). This interval spans the size of about 1221.5 cents.