Sevens.

[secca_pk]

No: HPFGUIDX 159660

Sarah  Barthell wrote:

> There are seven Weasley children: Bill, Charlie, Percy, Fred,
> George, Ron, and Ginny.

Secca adds:

Jo said somewhere in an interview that she was playing off the 
old "seventh son of a seventh son" myth... Ginny is the first female 
in a while in the Weasley family, and is the seventh daughter... 
which is one of the reasons she has posited for Ginny being such a 
powerful wizard... something that has been hinted at in the books so 
far, and something that might come in to play in "The-book-that-is-
yet-to-be-named."

/QUOTE:/ From the *same* Leaky Mug/Mugglenet interview , by Melissa 
and Emerson

JKR: The backstory with Ginny was, she was the first girl to arrive 
in the Weasley family in generations, but there's that old tradition 
of the seventh daughter of a seventh daughter and a seventh son of a 
seventh son, so that's why she's the seventh, because she is a 
gifted witch. I think you get hints of that, because she does some 
pretty impressive stuff here and there, and you'll see that again.
/End of QUOTE/


Secca again:
Hopefully it will be something more interesting than a really good 
bat-bogey hex...