Continuation of Friday 13th

Some of the superstition story said that,

Twelve gods were invited to a banquet at Valhalla. Loki, the Evil One, god of mischief, had been left off the guest list but crashed the party, bringing the total number of attendees to 13. True to character, Loki raised hell by inciting Hod, the blind god of winter, to attack Balder the Good, who was a favorite of the gods. Hod took a spear of mistletoe offered by Loki and obediently hurled it at Balder, killing him instantly.

All Valhalla grieved. And although one might take the moral of this story to be "Beware of uninvited guests bearing mistletoe," the Norse themselves apparently concluded that 13 people at a dinner party is just plain bad luck.

As if to prove the point, the Bible tells us there were exactly 13 present at the Last Supper. One of the dinner guests — disciples — betrayed Jesus Christ, setting the stage for the Crucifixion.
And did I mention the Crucifixion took place on a Friday? ;)