Three was a sacred number in ancient Celtic mythology and religion. Riddles and triadic phraseology are frequent in Celtic mythology. The triskel, a figure composed of three spirals, signifies the three-layered nature of a human soul, and is itself a central figure in ancient Celtic symbolism. The earth, sea, and sky were thought to share a three-fold marriage in oaths and as witness to deeds, and represented sacred elements.
Five: signified the family unit and order in Irish tradition, because of the five provinces of Ireland, and also the five laws imposed on provincial Irish kings.
Seventeen: was a number associated with the cycles of the visible moon, particularly the new moon. On this day of the moon's cycle, many influential and monumental events were thought to have taken place. The 17th generation was supposed to be the farthest reaches of ancestral memory, putting the longevity of memories within a clan at approximately 400 years.
Twenty-seven: represented the sacred number nine tripled three times, which supposedly triples its potency. Twenty-seven also signified the number of warriors comprising a war-band, and the number of the members of a Celtic chieftain's royal court. The number nine may also have been associated with a nine-day lunar week.
Thirty-three: represented the royal or judicary number, signifying great honor. The courts of great gods and heroes number thirty-two, with the king of the gods making the tally thirty-three. This also represented the number of islands that Maelduin had to visit before he could find his homeland.