644749 has 4 divisors (see below), whose sum is σ = 736864. Its totient is φ = 552636.

The previous prime is 644747. The next prime is 644753. The reversal of 644749 is 947446.

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: 947446 = 2 ⋅473723.

It is not a de Polignac number, because 644749 - 2¹ = 644747 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644747) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 46047 + ... + 46060.

It is an arithmetic number, because the mean of its divisors is an integer number (184216).

2⁶⁴⁴⁷⁴⁹ is an apocalyptic number.

It is an amenable number.

644749 is a deficient number, since it is larger than the sum of its proper divisors (92115).

644749 is an equidigital number, since it uses as much as digits as its factorization.

644749 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 92114.

The product of its digits is 24192, while the sum is 34.

The square root of 644749 is about 802.9626392305. The cubic root of 644749 is about 86.3900169221.

The spelling of 644749 in words is "six hundred forty-four thousand, seven hundred forty-nine".