644663709 has 12 divisors (see below), whose sum is σ = 940401852. Its totient is φ = 425520000.

The previous prime is 644663699. The next prime is 644663717. The reversal of 644663709 is 907366446.

644663709 is a `hidden beast` number, since 6 + 4 + 4 + 6 + 637 + 0 + 9 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 540562500 + 104101209 = 23250^2 + 10203^2 .

It is not a de Polignac number, because 644663709 - 2²⁵ = 611109277 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644663729) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 353692 + ... + 355509.

It is an arithmetic number, because the mean of its divisors is an integer number (78366821).

Almost surely, 2^644663709 is an apocalyptic number.

It is an amenable number.

644663709 is a deficient number, since it is larger than the sum of its proper divisors (295738143).

644663709 is a wasteful number, since it uses less digits than its factorization.

644663709 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 709308 (or 709305 counting only the distinct ones).

The product of its (nonzero) digits is 653184, while the sum is 45.

The square root of 644663709 is about 25390.2286125982. The cubic root of 644663709 is about 863.8620736942.

The spelling of 644663709 in words is "six hundred forty-four million, six hundred sixty-three thousand, seven hundred nine".