640645509 has 16 divisors (see below), whose sum is σ = 976652288. Its totient is φ = 365921712.

The previous prime is 640645501. The next prime is 640645513. The reversal of 640645509 is 905546046.

It is not a de Polignac number, because 640645509 - 2³ = 640645501 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 (640645501) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 55344 + ... + 65910.

It is an arithmetic number, because the mean of its divisors is an integer number (61040768).

Almost surely, 2^640645509 is an apocalyptic number.

It is an amenable number.

640645509 is a deficient number, since it is larger than the sum of its proper divisors (336006779).

640645509 is a wasteful number, since it uses less digits than its factorization.

640645509 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13464.

The product of its (nonzero) digits is 129600, while the sum is 39.

The square root of 640645509 is about 25310.9760578291. The cubic root of 640645509 is about 862.0635092804.

It can be divided in two parts, 6406 and 45509, that added together give a palindrome (51915).

The spelling of 640645509 in words is "six hundred forty million, six hundred forty-five thousand, five hundred nine".