Si5351 has output channel up to 8 and each output has one Multisynth divider (MS). Please note MS0 to MS5 can support fractional and integer divider (from 8~900) while MS6 and MS7 only support integer divider (even integer divider from 6~254) (please refer to AN619 for detail information).
In addition to 8-channel version (20 QFN package), Si5351 also has 3-channel version (10MSOP package) and 4-channel version (16QFN package). The MS of 3-channel version is from MS0 to MS2 normally for CLK0 to CLK2. While please pay attention to mapping relationship between output and MS divider for 4-channel version. MS divider of CLK0/CLK1/CLK2 and CLK3 is MS1/MS2/MS5 and MS7. This leads to CLK3 min frequency can’t as low as 2.5KHz like CLK0/1/2. 18.75KHz is the min output frequency for CLK3 for 3-channel version.