644395081 has 8 divisors (see below), whose sum is σ = 744328224. Its totient is φ = 551353920.

The previous prime is 644395069. The next prime is 644395091. The reversal of 644395081 is 180593446.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 644395081 - 2⁷ = 644394953 is a prime.

It is a super-2 number, since 2×644395081² = 830490040833993122, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644395001) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1722795 + ... + 1723168.

It is an arithmetic number, because the mean of its divisors is an integer number (93041028).

Almost surely, 2^644395081 is an apocalyptic number.

It is an amenable number.

644395081 is a deficient number, since it is larger than the sum of its proper divisors (99933143).

644395081 is a wasteful number, since it uses less digits than its factorization.

644395081 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3445991.

The product of its (nonzero) digits is 103680, while the sum is 40.

The square root of 644395081 is about 25384.9380735900. The cubic root of 644395081 is about 863.7420680862.

The spelling of 644395081 in words is "six hundred forty-four million, three hundred ninety-five thousand, eighty-one".