Claude GagniÃ¨re says in Au bonheur des mots:
The Italians fear the 17's, because 17 is written XVII in Roman numerals, which is the anagram of VIXI, which means "I lived", i.e. "I am dead". In Italy, buildings do not have a 17th floor, hotels do not have a room 17, and Alitalia planes do not have a seat 17 [neither do Air Inter planes and British Airways Concordes]. When Renault marketed its R17 and wanted to export it to Italy, it had to be renamed "Renault 177". Napoleon Bonaparte, who was more Italian than French in his education, refused to give the signal for his coup on "vendredi 17 brumaire" and postponed it until the following day.