645664621 has 12 divisors (see below), whose sum is σ = 775309440. Its totient is φ = 535573080.

The previous prime is 645664609. The next prime is 645664751. The reversal of 645664621 is 126466546.

It is not a de Polignac number, because 645664621 - 2⁹ = 645664109 is a prime.

It is a super-2 number, since 2×645664621² = 833765605622147282, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645664601) 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 11 ways as a sum of consecutive naturals, for example, 211011 + ... + 214048.

It is an arithmetic number, because the mean of its divisors is an integer number (64609120).

Almost surely, 2^645664621 is an apocalyptic number.

It is an amenable number.

645664621 is a deficient number, since it is larger than the sum of its proper divisors (129644819).

645664621 is a wasteful number, since it uses less digits than its factorization.

645664621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 425104 (or 425097 counting only the distinct ones).

The product of its digits is 207360, while the sum is 40.

The square root of 645664621 is about 25409.9315426075. The cubic root of 645664621 is about 864.3089231141.

The spelling of 645664621 in words is "six hundred forty-five million, six hundred sixty-four thousand, six hundred twenty-one".