I took from the book that the account number is actually 1-1-2-3-5-8-13-21 which is the Fibonacci sequence. The numbers that were written on the floor of the Louvre were just an "anagram" of this sequence.
Also, Sophie actually says that her grandfather "would have chosen an account number that had meaning to him, something he could easily remember"
Yeah - for the web quest [which I assume you're doing... ;-)] the account number is 1123581321 [the Fibonacci sequence in order]. As DOB says, the numbers that were written on the floor of the Louvre were just an "anagram" of this sequence.