644856081 has 8 divisors (see below), whose sum is σ = 860071200. Its totient is φ = 429772512.

The previous prime is 644856073. The next prime is 644856101. The reversal of 644856081 is 180658446.

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

It is not a de Polignac number, because 644856081 - 2³ = 644856073 is a prime.

It is a super-2 number, since 2×644856081² = 831678730405357122, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (644856041) 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, 20815 + ... + 41508.

It is an arithmetic number, because the mean of its divisors is an integer number (107508900).

Almost surely, 2^644856081 is an apocalyptic number.

It is an amenable number.

644856081 is a deficient number, since it is larger than the sum of its proper divisors (215215119).

644856081 is a wasteful number, since it uses less digits than its factorization.

644856081 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 65775.

The product of its (nonzero) digits is 184320, while the sum is 42.

The square root of 644856081 is about 25394.0166377830. The cubic root of 644856081 is about 863.9479925721.

The spelling of 644856081 in words is "six hundred forty-four million, eight hundred fifty-six thousand, eighty-one".