640869 has 4 divisors (see below), whose sum is σ = 854496. Its totient is φ = 427244.

The previous prime is 640859. The next prime is 640873. The reversal of 640869 is 968046.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 640869 - 2⁴ = 640853 is a prime.

It is a super-2 number, since 2×640869² = 821426150322, which contains 22 as substring.

It is a D-number.

It is a Curzon number.

640869 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640859) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 106809 + ... + 106814.

It is an arithmetic number, because the mean of its divisors is an integer number (213624).

2⁶⁴⁰⁸⁶⁹ is an apocalyptic number.

It is an amenable number.

640869 is a deficient number, since it is larger than the sum of its proper divisors (213627).

640869 is a wasteful number, since it uses less digits than its factorization.

640869 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 213626.

The product of its (nonzero) digits is 10368, while the sum is 33.

The square root of 640869 is about 800.5429407596. The cubic root of 640869 is about 86.2163742058.

The spelling of 640869 in words is "six hundred forty thousand, eight hundred sixty-nine".