668639 has 4 divisors (see below), whose sum is σ = 690240. Its totient is φ = 647040.

The previous prime is 668623. The next prime is 668671. The reversal of 668639 is 936866.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 668639 - 2⁴ = 668623 is a prime.

It is a super-2 number, since 2×668639² = 894156224642, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (668609) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 10754 + ... + 10815.

It is an arithmetic number, because the mean of its divisors is an integer number (172560).

2⁶⁶⁸⁶³⁹ is an apocalyptic number.

668639 is a deficient number, since it is larger than the sum of its proper divisors (21601).

668639 is a wasteful number, since it uses less digits than its factorization.

668639 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21600.

The product of its digits is 46656, while the sum is 38.

The square root of 668639 is about 817.7034914931. The cubic root of 668639 is about 87.4441112486. Note that the first 3 decimals are identical.

The spelling of 668639 in words is "six hundred sixty-eight thousand, six hundred thirty-nine".