640861 has 4 divisors (see below), whose sum is σ = 690172. Its totient is φ = 591552.

The previous prime is 640859. The next prime is 640873. The reversal of 640861 is 168046.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 47961 + 592900 = 219^2 + 770^2 .

It is not a de Polignac number, because 640861 - 2¹ = 640859 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 (640891) 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, 24636 + ... + 24661.

It is an arithmetic number, because the mean of its divisors is an integer number (172543).

2⁶⁴⁰⁸⁶¹ is an apocalyptic number.

It is an amenable number.

640861 is a deficient number, since it is larger than the sum of its proper divisors (49311).

640861 is a wasteful number, since it uses less digits than its factorization.

640861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 49310.

The product of its (nonzero) digits is 1152, while the sum is 25.

The square root of 640861 is about 800.5379441351. The cubic root of 640861 is about 86.2160154565.

The spelling of 640861 in words is "six hundred forty thousand, eight hundred sixty-one".