644021361 has 10 divisors (see below), whose sum is σ = 962056722. Its totient is φ = 429347520.

The previous prime is 644021291. The next prime is 644021381. The reversal of 644021361 is 163120446.

644021361 is a `hidden beast` number, since 6 + 440 + 213 + 6 + 1 = 666.

It can be written as a sum of positive squares in only one way, i.e., 642318336 + 1703025 = 25344^2 + 1305^2 .

It is not a de Polignac number, because 644021361 - 2⁷ = 644021233 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (644021381) by changing a digit.

It is a polite number, since it can be written in 9 ways as a sum of consecutive naturals, for example, 3975360 + ... + 3975521.

Almost surely, 2^644021361 is an apocalyptic number.

It is an amenable number.

644021361 is a deficient number, since it is larger than the sum of its proper divisors (318035361).

644021361 is an equidigital number, since it uses as much as digits as its factorization.

644021361 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7950893 (or 7950884 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 27.

The square root of 644021361 is about 25377.5759480688. The cubic root of 644021361 is about 863.5750586857.

The spelling of 644021361 in words is "six hundred forty-four million, twenty-one thousand, three hundred sixty-one".