F1 suffers from triskaidekaphobia:
An abnormal fear of the number thirteen.

"The last time is was used in F1 was by she-racer Divina Galica was a well-known Olympic skier.

In 1976 she was entered for the British Shellsport International Group 8 series and after some promising performances, Nick Whiting decided to enter her for the British Grand Prix. It was the first time in 13 years a car with the No. 13 had been seen at a race, but Galica failed to qualify."


Source: http://en.espnf1.com/hesketh/motorsport/driver/1011.html#IaWTiWbpBYDXL3Lw.99