644720605 has 16 divisors (see below), whose sum is σ = 801187200. Its totient is φ = 497465920.

The previous prime is 644720603. The next prime is 644720641. The reversal of 644720605 is 506027446.

It is not a de Polignac number, because 644720605 - 2¹ = 644720603 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644720603) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 189570 + ... + 192940.

It is an arithmetic number, because the mean of its divisors is an integer number (50074200).

Almost surely, 2^644720605 is an apocalyptic number.

It is an amenable number.

644720605 is a deficient number, since it is larger than the sum of its proper divisors (156466595).

644720605 is a wasteful number, since it uses less digits than its factorization.

644720605 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4724.

The product of its (nonzero) digits is 40320, while the sum is 34.

The square root of 644720605 is about 25391.3490189080. The cubic root of 644720605 is about 863.8874868670.

The spelling of 644720605 in words is "six hundred forty-four million, seven hundred twenty thousand, six hundred five".