640335521621 has 4 divisors (see below), whose sum is σ = 674037391200. Its totient is φ = 606633652044.

The previous prime is 640335521611. The next prime is 640335521633. The reversal of 640335521621 is 126125533046.

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 640335521621 - 2¹⁴ = 640335505237 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 (640335521611) 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, 16850934761 + ... + 16850934798.

It is an arithmetic number, because the mean of its divisors is an integer number (168509347800).

Almost surely, 2^640335521621 is an apocalyptic number.

It is an amenable number.

640335521621 is a deficient number, since it is larger than the sum of its proper divisors (33701869579).

640335521621 is a wasteful number, since it uses less digits than its factorization.

640335521621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 33701869578.

The product of its (nonzero) digits is 129600, while the sum is 38.

The spelling of 640335521621 in words is "six hundred forty billion, three hundred thirty-five million, five hundred twenty-one thousand, six hundred twenty-one".