640861621 has 4 divisors (see below), whose sum is σ = 674591200. Its totient is φ = 607132044.

The previous prime is 640861609. The next prime is 640861681. The reversal of 640861621 is 126168046.

640861621 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 a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 640861621 - 2⁷ = 640861493 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640861681) 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, 16864761 + ... + 16864798.

It is an arithmetic number, because the mean of its divisors is an integer number (168647800).

Almost surely, 2^640861621 is an apocalyptic number.

It is an amenable number.

640861621 is a deficient number, since it is larger than the sum of its proper divisors (33729579).

640861621 is a wasteful number, since it uses less digits than its factorization.

640861621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 33729578.

The product of its (nonzero) digits is 13824, while the sum is 34.

The square root of 640861621 is about 25315.2448338941. The cubic root of 640861621 is about 862.1604330454.

The spelling of 640861621 in words is "six hundred forty million, eight hundred sixty-one thousand, six hundred twenty-one".