644885381 has 4 divisors (see below), whose sum is σ = 737011872. Its totient is φ = 552758892.

The previous prime is 644885317. The next prime is 644885387. The reversal of 644885381 is 183588446.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 183588446 = 2 ⋅91794223.

It is not a de Polignac number, because 644885381 - 2⁶ = 644885317 is a prime.

It is a super-2 number, since 2×644885381² = 831754309255030322, 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 (644885387) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 46063235 + ... + 46063248.

It is an arithmetic number, because the mean of its divisors is an integer number (184252968).

Almost surely, 2^644885381 is an apocalyptic number.

It is an amenable number.

644885381 is a deficient number, since it is larger than the sum of its proper divisors (92126491).

644885381 is an equidigital number, since it uses as much as digits as its factorization.

644885381 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 92126490.

The product of its digits is 737280, while the sum is 47.

The square root of 644885381 is about 25394.5935387830. The cubic root of 644885381 is about 863.9610772968.

The spelling of 644885381 in words is "six hundred forty-four million, eight hundred eighty-five thousand, three hundred eighty-one".