636

636 is a natural number that comes after 635 and before 637. In mathematics and everyday use, it is most commonly encountered as a composite integer and a multiple of several smaller integers.

In mathematics, 636 factors as 2^2 × 3 × 53. It is divisible by 1, 2, 3, 4, 6, 12, 53, 106, 159, 212, 318, and 636, yielding 12 divisors in total. The digit sum is 15, so it is divisible by 3 but not by 9. It is an even number and thus divisible by 2.

In telecommunications, 636 is an area code in Missouri that covers western and northern suburbs of St. Louis. It was created as a split from the nearby 314 area code and serves several counties and communities in the region; ten-digit dialing is common in that area.

In astronomy, 636 Erika is a main-belt asteroid. As a small celestial body, it is one of the numerous catalogued objects orbiting the Sun between Mars and Jupiter.

In history, 636 CE marks a year during the early medieval period. Notable events include the Battle of Yarmouk, a major conflict between the Rashidun Caliphate and the Byzantine Empire that contributed to the expansion of Islam into the Levant.