645206621 has 4 divisors (see below), whose sum is σ = 645269472. Its totient is φ = 645143772.

The previous prime is 645206581. The next prime is 645206623. The reversal of 645206621 is 126602546.

645206621 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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 645206621 - 2²⁶ = 578097757 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 (645206623) 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, 12041 + ... + 37886.

It is an arithmetic number, because the mean of its divisors is an integer number (161317368).

Almost surely, 2^645206621 is an apocalyptic number.

It is an amenable number.

645206621 is a deficient number, since it is larger than the sum of its proper divisors (62851).

645206621 is a wasteful number, since it uses less digits than its factorization.

645206621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 62850.

The product of its (nonzero) digits is 17280, while the sum is 32.

The square root of 645206621 is about 25400.9177196415. The cubic root of 645206621 is about 864.1045099095.

The spelling of 645206621 in words is "six hundred forty-five million, two hundred six thousand, six hundred twenty-one".