jezbowman, broadcast band AM station frequencies all are divisible by 9 - it's the way their frequency spectrum is split up and allocated. Analogous to our VHF 8.33Mhz spacing. I imagine that NDBs use a lot less bandwidth, so can be closer in frequency without interfering.
As an aside, that pearl of the Pacific, KUMU1500 in HNL, has gone from music to yap-yap. Pity, even though the music was far away from rock or even modern, it was something to listen to and available over a wide area of the Pacific.
Let's have a post from anyone who knows of any AM station worth listening to so we can all benefit.