The Enoch calendar is an ancient calendar described in the pseudepigraphal Book of Enoch. It divided the year into four seasons of exactly 13 weeks. Each season consisted of two 30-day months followed by one 31-day month, with the 31st day ending the season, so that Enoch’s year consisted of exactly 364 days.
The Enoch calendar was purportedly given to Enoch by the angel Uriel. Four named days, inserted as the 31st day of every third month, were named instead of numbered, which “placed them outside the numbering”. The Book of Enoch gives the count of 2,912 days for 8 years, which divides out to exactly 364 days per year. This specifically excludes any periodic intercalations.