645321621 has 24 divisors (see below), whose sum is σ = 1002326304. Its totient is φ = 368232480.

The previous prime is 645321619. The next prime is 645321631. The reversal of 645321621 is 126123546.

It is not a de Polignac number, because 645321621 - 2¹ = 645321619 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645321631) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 116511 + ... + 121923.

It is an arithmetic number, because the mean of its divisors is an integer number (41763596).

Almost surely, 2^645321621 is an apocalyptic number.

It is an amenable number.

645321621 is a deficient number, since it is larger than the sum of its proper divisors (357004683).

645321621 is a wasteful number, since it uses less digits than its factorization.

645321621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6241 (or 6234 counting only the distinct ones).

The product of its digits is 8640, while the sum is 30.

The square root of 645321621 is about 25403.1813165202. The cubic root of 645321621 is about 864.1558454621.

The spelling of 645321621 in words is "six hundred forty-five million, three hundred twenty-one thousand, six hundred twenty-one".