http://www.interactive-radio-system.com ... andard.pdf
See page 42.
By the way, some AM (MW) frequencies (those above 1602) cannot even be encoded this way!
I'm guessing that the LW part is also different in the US. So far I couldn't find an RDBS spec. (Hm. I could just connect an analyzer and let it check things in RDBS mode... -> Edit: No, RDSSpy only supports RDS and not RDBS, apparently
)
By the way, (1602 - 531) / 9 * 10 + 530 = 1720. So all the codes upto 1720 should be encodable this way, assuming that there aren't more LW freqs.