The 74185 is a binary-to-BCD converter. It is designed cleverly utilizing the fact that both 10 and 2^n are divisible by 2 once, thereby omitting processing of the LSB entirely. More interestingly even is that it can be cascaded to display arbitrary length digits.
The TI datasheet shows multiple configurations, for 6, 8, 9, 12, and 16 bit inputs. Though there clearly is a pattern of how to design those, it eludes me for the lower bit numbers. I cannot understand what is actually going on, understand why the circuit actually works and can be cascaded in the fashion shown in the datasheet. Can you explain how to come up with the cascade design and why it works?