644858623 has 6 divisors (see below), whose sum is σ = 652728584. Its totient is φ = 637082436.

The previous prime is 644858597. The next prime is 644858657. The reversal of 644858623 is 326858446.

It is not a de Polignac number, because 644858623 - 2²⁵ = 611304191 is a prime.

It is a super-2 number, since 2×644858623² = 831685287314912258, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644858663) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 39915 + ... + 53692.

Almost surely, 2^644858623 is an apocalyptic number.

644858623 is a deficient number, since it is larger than the sum of its proper divisors (7869961).

644858623 is an frugal number, since it uses more digits than its factorization.

644858623 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 93773 (or 93690 counting only the distinct ones).

The product of its digits is 1105920, while the sum is 46.

The square root of 644858623 is about 25394.0666888941. The cubic root of 644858623 is about 863.9491277882.

The spelling of 644858623 in words is "six hundred forty-four million, eight hundred fifty-eight thousand, six hundred twenty-three".