64:81:96 is a major triad found on the I, IV, and V of the 3-limit diatonic scale. It is easily referred to as the Pythagorean major triad, and, unlike 4:5:6, 54:64:81 is ambitonal.

Chord information
Harmonics 64:81:96
Subharmonics 1/(81:64:54)
Intervals from root 1/181/643/2
Cents from root 408¢702¢
Step intervals 81/64, 32/27
Step cents 408¢, 294¢
Color name lawa or Lw
Prime limit 3
Genus 34 (81)
Intervallic odd limit 81
Otonal odd limit 81
Utonal odd limit 81
Consistent edos (d ≥ 2) 12edo**, 17edo*, 24edo*, 29edo*, …

In meantone this chord is tempered together with 4:5:6; it may be considered a 3-limit approximation of that chord, or used in its own right as a chord with a less stable third. Accordingly, Aura takes advantage of these properties in his non-meantone 5-limit music where it shows up as the triad built on the IV degree in Ionian mode, thus preventing that scale degree from being tonicized by accident and lessening tonal ambiguity in plagal and semiplagal cadences, as well as other chord progressions that use both I and IV.