66 (number)
From Halbeeg, the open encyclopedia · Af-Soomaali
80 languages
66 is a natural number that follows 65 and precedes 67. It is the fifty-sixth number when counted from one, and it is even because it is divisible by two without remainder.
In the decimal number system, 66 is written with two digits: sixty-six. In Roman numerals it is written LXVI. In binary it is 1000010.
Mathematical properties
66 is a composite number, not a prime number. Its divisors are 1, 2, 3, 6, 11, 22, 33, and 66. When broken down into prime factors it becomes 2 × 3 × 11, making it a number with three distinct prime divisors.
66 is a triangular number, since it equals the sum of the integers from 1 to 11: 1+2+3+…+11 = 66. It is also a hexagonal number, derived from the formula n(2n−1) when n = 6.
When its proper divisors (those less than 66 itself) are added together, their sum exceeds 66, and so 66 is counted among the abundant numbers. The sum of its two digits is 12, which is divisible by 3, showing that 66 is also divisible by 3.
Common use
66 is used in counting, measurement, and reference for purposes such as age, year, route number, or code number. Like other numbers, its use in relation to specific symbols (such as road numbers or codes) depends on the system of each country or organization.