366

366 is the natural number that follows 365 and precedes 367. It is an even composite number with prime factorization 2 × 3 × 61. Its positive divisors are 1, 2, 3, 6, 61, 122, 183, and 366. The sum of its proper divisors is 378, so 366 is an abundant number. It is also a sphenic number, since it is the product of three distinct primes (2, 3, and 61).

In representations, 366 is written as CCCLXVI in Roman numerals. In binary, it equals 101101110.

In calendar terms, 366 is the number of days in a leap year in the Gregorian calendar. Leap years occur to align the calendar year with the Earth's orbit, using the rule that years divisible by 4 are leap years, except century years not divisible by 400. Thus most leap years add an extra day to February, resulting in 366 days for that year.