Any significance to the number 13?
Some superstitious people believe 13 is a bad luck number. I'm not superstitious but a lot of people believe this is true. Especially Friday the thirteenth.
Advertising manuals urge businesses to avoid using this number. Some hotels and buildings don't have a thirteenth floor. There is a 12th and a 14th floor but no 13.
Other references to the number in the film. Launched on the thirteenth etc.
It was pretty unlucky they had that malfunction when it did and spoiled the mission.
SPOILER
It is also lucky (with heroic and skillful teamwork) the men made it back and were OK.
An outstanding film.
What if they named it Apollo 14 and didn't launch on the thirteenth?