In chapter 11 of Harry Potter and the Prisoner of Azkaban, Dumbledore invites Trelawney to join his Christmas dinner in The Great Hall.
She declined, saying,
"I dare not, Headmaster! If I join the table, we shall be thirteen! Nothing could be more unlucky! Never forget that when thirteen dine together, the first to rise will be the first to die!"
She thought there were 12 people at the table, but if you count Scabbers the rat (secretly Peter Pettigrew in disguise), then there were already 13 dining together. Dumbledore was the first to rise and he was the first to die when Snape killed him at the top of the Observation Tower.
In chapter 5 of Harry Potter and the Order of the Phoenix, 13 people dined together at 12 Grimauld Place. Sirius Black was the first person to rise from the table.
Sirius started to rise from his chair.
"Molly, you're not the only person at this table who cares about Harry," said Lupin sharply.
"Sirius, sit down." Mrs. Weasley's lower lip was trembling.
Sirius sank slowly back into his chair, his face white.
Sirius was killed by his cousin, Bellatrix Lestrange, later in the same book.
How many other occurrences were there in the Harry Potter stories of 13 people dining together? And was the first to rise always the first to die among them?