Jackson and the Number Seven

My favorite number is seven. Jackson's favorite number is three and apparently Jackson's least favorite number is seven. Whenever we count with him, he always skips the number seven. At his last Kids On the Move visit, I explained this to Marsha and she took it to task to get him to say the number seven. Here's what happened, as related to Nate through Google Talk:

Me:
So get this- we were doing counting with Jackson and he was skipping #7 like usual.
So then Marsha had him stack blocks and count them and he still skipped #7.
And then she was helping him count the stacked blocks, touching each one as they counted, and he not only skipped saying #7, he even skipped over touching the 7th block.

Nate:
Wow.

Me:
So then, just as an experiment, she tried getting him to say seven in Spanish figuring he wouldn't know that siete was seven. So we are counting uno, dos, tres, etc. and when we say siete, Jackson instead says ocho. No lie. I don't even know how he would know 8 in Spanish since he doesn't watch Dora (or Diego) like Jefferson did.
Jackson seems to want to believe that the number 7 does not exist- kind-of like the number thirteen in buildings.