The image above is a functional chord symbol. But what does the number mean?
Lower-case 'i' means the tonic chord of a minor key. The superscript '6' means first inversion. Intervals of a 6th and a third above the lowest note (the '3' is assumed.)
Note that 'Cm6' (with an explicit letter-name) means something different. That's 'C minor sixth', a C minor triad with an added A.