640823 has 8 divisors (see below), whose sum is σ = 664848. Its totient is φ = 617344.

The previous prime is 640793. The next prime is 640837. The reversal of 640823 is 328046.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a de Polignac number, because none of the positive numbers 2^k-640823 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640853) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5615 + ... + 5727.

It is an arithmetic number, because the mean of its divisors is an integer number (83106).

2⁶⁴⁰⁸²³ is an apocalyptic number.

640823 is a deficient number, since it is larger than the sum of its proper divisors (24025).

640823 is a wasteful number, since it uses less digits than its factorization.

640823 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 273.

The product of its (nonzero) digits is 1152, while the sum is 23.

The square root of 640823 is about 800.5142097427. The cubic root of 640823 is about 86.2143113567.

Adding to 640823 its reverse (328046), we get a palindrome (968869).

The spelling of 640823 in words is "six hundred forty thousand, eight hundred twenty-three".