640665853 has 4 divisors (see below), whose sum is σ = 642003840. Its totient is φ = 639327868.

The previous prime is 640665833. The next prime is 640665869. The reversal of 640665853 is 358566046.

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.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-640665853 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 (640665833) 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, 668275 + ... + 669232.

It is an arithmetic number, because the mean of its divisors is an integer number (160500960).

Almost surely, 2^640665853 is an apocalyptic number.

It is an amenable number.

640665853 is a deficient number, since it is larger than the sum of its proper divisors (1337987).

640665853 is a wasteful number, since it uses less digits than its factorization.

640665853 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1337986.

The product of its (nonzero) digits is 518400, while the sum is 43.

The square root of 640665853 is about 25311.3779356241. The cubic root of 640665853 is about 862.0726342615.

The spelling of 640665853 in words is "six hundred forty million, six hundred sixty-five thousand, eight hundred fifty-three".