???

While I was out and about on the roads yesterday, I saw the following license plate: DX3NING

And then proceeded to spend the next twenty minutes trying to guess what that might mean. (And then I googled it this morning, but just got some non-english math links. Although if that's what they were going for, I'm impressed, I guess? I'm not a math person.)

I feel like I must be missing something obvious. Sometimes I can figure them out! But I've got nothing on this one.