It is a happy number.
668999 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.
It is a weak prime.
It is a cyclic number.
It is a de Polignac number, because none of the positive numbers 2k-668999 is a prime.
It is a plaindrome in base 10.
It is a congruent number.
2668999 is an apocalyptic number.
668999 is an equidigital number, since it uses as much as digits as its factorization.
668999 is an evil number, because the sum of its binary digits is even.
The square root of 668999 is about 817.9235905633. The cubic root of 668999 is about 87.4598019437.
The spelling of 668999 in words is "six hundred sixty-eight thousand, nine hundred ninety-nine".