644028681 has 8 divisors (see below), whose sum is σ = 896040000. Its totient is φ = 410684912.

The previous prime is 644028661. The next prime is 644028709. The reversal of 644028681 is 186820446.

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 644028681 - 2²¹ = 641931529 is a prime.

It is a super-2 number, since 2×644028681² = 829545883901199522, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (644028611) 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, 4666806 + ... + 4666943.

It is an arithmetic number, because the mean of its divisors is an integer number (112005000).

Almost surely, 2^644028681 is an apocalyptic number.

It is an amenable number.

644028681 is a deficient number, since it is larger than the sum of its proper divisors (252011319).

644028681 is a wasteful number, since it uses less digits than its factorization.

644028681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9333775.

The product of its (nonzero) digits is 73728, while the sum is 39.

The square root of 644028681 is about 25377.7201694715. The cubic root of 644028681 is about 863.5783304952.

The spelling of 644028681 in words is "six hundred forty-four million, twenty-eight thousand, six hundred eighty-one".