668640 has 96 divisors (see below), whose sum is σ = 2419200. Its totient is φ = 152064.

The previous prime is 668623. The next prime is 668671. The reversal of 668640 is 46866.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (96).

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a junction number, because it is equal to n+sod(n) for n = 668598 and 668607.

It is a congruent number.

It is an unprimeable number.

668640 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3261 + ... + 3459.

It is an arithmetic number, because the mean of its divisors is an integer number (25200).

2⁶⁶⁸⁶⁴⁰ is an apocalyptic number.

668640 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 668640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1209600).

668640 is an abundant number, since it is smaller than the sum of its proper divisors (1750560).

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

668640 is a wasteful number, since it uses less digits than its factorization.

668640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 224 (or 216 counting only the distinct ones).

The product of its (nonzero) digits is 6912, while the sum is 30.

The square root of 668640 is about 817.7041029615. The cubic root of 668640 is about 87.4441548417. Note that the first 3 decimals are identical.

The spelling of 668640 in words is "six hundred sixty-eight thousand, six hundred forty".