Sevens.

[sara griffin]

No: HPFGUIDX 159860


Secca:
> 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, <snip>


Sara:       
Not sure if it quite fits into the theory, but in HBP the potion 
Harry makes that wins him the luck potion was stirred once 
anticlockwise after being stirred seven times clockwise ??