12:14:18:21

The swiss tetrad is a just 7-prime-limit, 9-odd-limit chord which is an ASS, or anomalous saturated suspension. In close position, it is 1-7/6-3/2-7/4, with steps 7/6-9/7-7/6-8/7. Tempered versions of it have been called "subminor seventh chords" or "swiss sixth chords", so "swiss tetrad" splits the difference.