644657731 has 16 divisors (see below), whose sum is σ = 714222144. Its totient is φ = 578755584.

The previous prime is 644657729. The next prime is 644657737. The reversal of 644657731 is 137756446.

It is a cyclic number.

It is not a de Polignac number, because 644657731 - 2¹ = 644657729 is a prime.

It is a super-2 number, since 2×644657731² = 831167180276136722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644657737) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 153151 + ... + 157303.

It is an arithmetic number, because the mean of its divisors is an integer number (44638884).

Almost surely, 2^644657731 is an apocalyptic number.

644657731 is a deficient number, since it is larger than the sum of its proper divisors (69564413).

644657731 is a wasteful number, since it uses less digits than its factorization.

644657731 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4590.

The product of its digits is 423360, while the sum is 43.

The square root of 644657731 is about 25390.1108898721. The cubic root of 644657731 is about 863.8594034733.

The spelling of 644657731 in words is "six hundred forty-four million, six hundred fifty-seven thousand, seven hundred thirty-one".