640769 has 4 divisors (see below), whose sum is σ = 648960. Its totient is φ = 632580.

The previous prime is 640741. The next prime is 640771. The reversal of 640769 is 967046.

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: 967046 = 2 ⋅483523.

It is a cyclic number.

It is not a de Polignac number, because 640769 - 2¹² = 636673 is a prime.

It is a super-2 number, since 2×640769² = 821169822722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (640069) 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, 3977 + ... + 4134.

It is an arithmetic number, because the mean of its divisors is an integer number (162240).

2⁶⁴⁰⁷⁶⁹ is an apocalyptic number.

It is an amenable number.

640769 is a deficient number, since it is larger than the sum of its proper divisors (8191).

640769 is an equidigital number, since it uses as much as digits as its factorization.

640769 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8190.

The product of its (nonzero) digits is 9072, while the sum is 32.

The square root of 640769 is about 800.4804807114. The cubic root of 640769 is about 86.2118896253.

The spelling of 640769 in words is "six hundred forty thousand, seven hundred sixty-nine".