640923 has 4 divisors (see below), whose sum is σ = 854568. Its totient is φ = 427280.

The previous prime is 640919. The next prime is 640933. The reversal of 640923 is 329046.

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 640923 - 2² = 640919 is a prime.

It is a D-number.

It is a junction number, because it is equal to n+sod(n) for n = 640893 and 640902.

It is not an unprimeable number, because it can be changed into a prime (640933) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 106818 + ... + 106823.

It is an arithmetic number, because the mean of its divisors is an integer number (213642).

2⁶⁴⁰⁹²³ is an apocalyptic number.

640923 is a deficient number, since it is larger than the sum of its proper divisors (213645).

640923 is a wasteful number, since it uses less digits than its factorization.

640923 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 213644.

The product of its (nonzero) digits is 1296, while the sum is 24.

The square root of 640923 is about 800.5766671594. The cubic root of 640923 is about 86.2187956853.

Adding to 640923 its reverse (329046), we get a palindrome (969969).

The spelling of 640923 in words is "six hundred forty thousand, nine hundred twenty-three".