They're a bit mask, with the LSB always set. The values are 100001 (33), 011001 (25), 010001 (17), and 001001 (9). And they're probably ORed with other values so multiple parameters can be set with a single word.

Best guess: either (1) it maps to internal values that macOS uses, or (2) they wanted to build in the potential to have more granular values later.