Ferrari gave lower number to Raikkonen although he finished behind Massa in last year championship, perhaps because Raikkonen has already won one title. Or maybe the reason is that Kimi gets paid much more than Massa

Red Bull are another case – Vettel finished ahead of Webber last year, but perhaps because Vettel is new in Red Bull Racing the lower number went to Webber. It also does not mean Webber will be Red Bull’s number 1 and Vettel number 2 next year

“The number 13 hasn’t been used in a Grand Prix since the numbering system for cars was first formalised in the mid 70’s. Most of Formula One teams are based in Britain, and racers are a superstitious bunch. So 13 has been skipped. Occasionally #14 has been skipped as well so teams can have the odd-even combination. Mostly though it’s superstition, and over a period of at least 30 years that superstitious belief has become habit.”

However there were cases of number 13 in F1:

1963 – Mexican GP – http://en.wikipedia.org/wiki/1963_Mexican_Grand_Prix

1976 – British GP – http://en.wikipedia.org/wiki/1976_British_Grand_Prix

I’m not that big guru of F1, I just got informed: http://translate.google.com/translate?u=http%3A%2F%2Fwww.cronicas-formula1.com%2F2008%2F01%2Fsupersticiones-el-piloto-n-13-en-frmula.html&sl=es&tl=en&hl=es&ie=UTF-8

Some seasons the jumps between driver’s numbers were bigger, like in ’89 when there weren’t number 13 (usual) and 14 (?). Or in 1980, when Williams F1 were gifted with the very last numbers 43, 50 and 51 (???), actually that season 3 drivers shared the same number in different parts of the year, the 43(!!!).
What I do not like much is that in a main driver relay by a test-diver or a driver replacement, the coming driver use the same number, which isn’t faithful to his quality ranking. For example look back 2006, Pedro De la Rosa was driver 4 after Montoya left the team.

The thing is… Driver lists never have been too much accurate, and the means of placing them in a ranking based on the previous season aren’t just real if considering guys which have been champions and years after the last monkey in the grid (an example could be Jacques Villeneuve).
This number list just helps to create a control system based on their numbers for stewards, timekeepers, marshals, and of course broadcast TV. This is much easier than following the names written on the bodywork.

I think keeping the number 13 away from the list is a stupid joke, but if the FIA and the contesting teams want it so… Then who will change that superstition myth?