I (Inthar) view 21edo in two ways:

  1. Viewed more traditionally, it's a "color system" with traditional triadic harmony, 7edo circles of fifths, and many interesting colors for intervals.
  2. As a MOS system, its most interesting MOS scales are soft oneirotonic and superhard orwelloid.

Intervals

Degree Cents Up/down notation Fox-Raven
5L3s Octotonic
Notation
Category name
0 0.00 1 unison C N
1 57.14 ^1
vv2
up unison,
double-down 2nd
^C
vvD
N#/Ob Subminor 2nd
2 114.29 ^^1
v2
double-up unison,
down 2nd
^^C
vD
O Minor 2nd
3 171.43 2 hepta 2nd D O# Submajor 2nd
4 228.57 ^2
vv3
up 2nd,
double-down 3rd
^D
vvE
Pb Supermajor 2nd
5 285.71 ^^2
v3
double-up 2nd,
down 3rd
^^D
vE
P Minor 3rd
6 342.86 3 hepta 3rd E P#/Qb Neutral 3rd
7 400.00 ^3
vv4
up 3rd,
double-down 4th
^E
vvF
Q Major 3rd
8 457.14 ^^3
v4
double-up 3rd,
down 4th
^^E
vF
Q# Naiadic; Subfourth
9 514.29 4 hepta 4th F Jb Perfect 4th
10 571.43 ^4
vv5
up 4th,
double-down 5th
^F
vvG
J Narrow Tritone
11 628.57 ^^4
v5
double-up 4th,
down 5th
^^F
vG
J# Wide Tritone
12 685.71 5 hepta 5th G Kb Perfect 5th
13 742.86 ^5
vv6
up 5th,
double-down 6th
^G
vvA
K Superfifth
14 800.00 ^^5
v6
double-up 5th,
down 6th
^^G
vA
K#/Lb Minor 6th
15 857.14 6 hepta 6th A L Neutral 6th
16 914.29 ^6
vv7
up 6th,
double-down 7th
^A
vvB
L# Major 6th
17 971.43 ^^6
v7
double-up 6th,
down 7th
^^A
vB
Mb Subminor 7th
18 1028.57 7 hepta 7th B M Supraminor 7th
19 1085.71 ^7
vv8
up 7th,
double-down 8ve
^B
vvC
M# Major 7th
20 1142.86 ^^7
v8
double-up 7th,
down 8ve
^^B
vC
Nb Supermajor 7th
21 1200.00 8 8ve C N Octave