I was wondering what the studio names mean in Idolm@ster, and DiGiKerot said:

<DiGiKerot> The trick is that the character for 6 can be pronounced Mu or Mutsu or similar, so it contracts to NaMuGo, or, rather, Namco, the name of the developer of the iM@S games.
<DiGiKerot> I think 961 is supposed to be Kuroi

I began to pay attention when I noticed the fans' outrage over the defection of Miki to 961 Studios in the PSP version. BTW, I'm pretty sure I've seen the "961" moniker in some entirely unrelated anime, but cannot remember which one it was.

UPDATE: Andy writes:

Hm... Keroro maybe? I know they're constantly doing 723 and 623 for Natsumi and Mutsumi...

Do they make a Keroro game? I don't know.