640997 has 4 divisors (see below), whose sum is σ = 732576. Its totient is φ = 549420.

The previous prime is 640993. The next prime is 641051. The reversal of 640997 is 799046.

It is a happy number.

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, and also an emirpimes, since its reverse is a distinct semiprime: 799046 = 2 ⋅399523.

It is a cyclic number.

It is not a de Polignac number, because 640997 - 2² = 640993 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 (640993) 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, 45779 + ... + 45792.

It is an arithmetic number, because the mean of its divisors is an integer number (183144).

2⁶⁴⁰⁹⁹⁷ is an apocalyptic number.

It is an amenable number.

640997 is a deficient number, since it is larger than the sum of its proper divisors (91579).

640997 is an equidigital number, since it uses as much as digits as its factorization.

640997 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 91578.

The product of its (nonzero) digits is 13608, while the sum is 35.

The square root of 640997 is about 800.6228825109. The cubic root of 640997 is about 86.2221137882. Note that the first 3 decimals are identical.

The spelling of 640997 in words is "six hundred forty thousand, nine hundred ninety-seven".