666640720 has 80 divisors (see below), whose sum is σ = 1657393920. Its totient is φ = 248481792.

The previous prime is 666640697. The next prime is 666640753. The reversal of 666640720 is 27046666.

666640720 is digitally balanced in base 6, because in such base it contains all the possibile digits an equal number of times.

It is a tau number, because it is divible by the number of its divisors (80).

It is a self number, because there is not a number n which added to its sum of digits gives 666640720.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 137701 + ... + 142459.

It is an arithmetic number, because the mean of its divisors is an integer number (20717424).

Almost surely, 2^666640720 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 666640720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (828696960).

666640720 is an abundant number, since it is smaller than the sum of its proper divisors (990753200).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

666640720 is a wasteful number, since it uses less digits than its factorization.

666640720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4892 (or 4886 counting only the distinct ones).

The product of its (nonzero) digits is 72576, while the sum is 37.

The square root of 666640720 is about 25819.3865147877. The cubic root of 666640720 is about 873.5691313387.

The spelling of 666640720 in words is "six hundred sixty-six million, six hundred forty thousand, seven hundred twenty".