640989 has 12 divisors (see below), whose sum is σ = 940576. Its totient is φ = 420552.

The previous prime is 640973. The next prime is 640993. The reversal of 640989 is 989046.

640989 is a `hidden beast` number, since 640 + 9 + 8 + 9 = 666.

It is not a de Polignac number, because 640989 - 2⁴ = 640973 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640919) 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 11 ways as a sum of consecutive naturals, for example, 72 + ... + 1134.

2⁶⁴⁰⁹⁸⁹ is an apocalyptic number.

It is an amenable number.

640989 is a deficient number, since it is larger than the sum of its proper divisors (299587).

640989 is a wasteful number, since it uses less digits than its factorization.

640989 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1136 (or 1133 counting only the distinct ones).

The product of its (nonzero) digits is 15552, while the sum is 36.

The square root of 640989 is about 800.6178863853. The cubic root of 640989 is about 86.2217550867.

The spelling of 640989 in words is "six hundred forty thousand, nine hundred eighty-nine".