644634491 has 4 divisors (see below), whose sum is σ = 665429184. Its totient is φ = 623839800.

The previous prime is 644634443. The next prime is 644634499. The reversal of 644634491 is 194436446.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 644634491 - 2⁶ = 644634427 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644634499) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 10397300 + ... + 10397361.

It is an arithmetic number, because the mean of its divisors is an integer number (166357296).

Almost surely, 2^644634491 is an apocalyptic number.

644634491 is a deficient number, since it is larger than the sum of its proper divisors (20794693).

644634491 is a wasteful number, since it uses less digits than its factorization.

644634491 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20794692.

The product of its digits is 248832, while the sum is 41.

The square root of 644634491 is about 25389.6532272499. The cubic root of 644634491 is about 863.8490225984.

The spelling of 644634491 in words is "six hundred forty-four million, six hundred thirty-four thousand, four hundred ninety-one".