640397 has 4 divisors (see below), whose sum is σ = 642396. Its totient is φ = 638400.

The previous prime is 640369. The next prime is 640411. The reversal of 640397 is 793046.

640397 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 793046 = 2 ⋅396523.

It can be written as a sum of positive squares in 2 ways, for example, as 434281 + 206116 = 659^2 + 454^2 .

It is a cyclic number.

It is not a de Polignac number, because 640397 - 2⁶ = 640333 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 (640307) 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, 398 + ... + 1199.

It is an arithmetic number, because the mean of its divisors is an integer number (160599).

2⁶⁴⁰³⁹⁷ is an apocalyptic number.

It is an amenable number.

640397 is a deficient number, since it is larger than the sum of its proper divisors (1999).

640397 is a wasteful number, since it uses less digits than its factorization.

640397 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1998.

The product of its (nonzero) digits is 4536, while the sum is 29.

The square root of 640397 is about 800.2480865332. The cubic root of 640397 is about 86.1952028884.

It can be divided in two parts, 64039 and 7, that added together give a palindrome (64046).

The spelling of 640397 in words is "six hundred forty thousand, three hundred ninety-seven".