644723 has 4 divisors (see below), whose sum is σ = 649200. Its totient is φ = 640248.

The previous prime is 644717. The next prime is 644729. The reversal of 644723 is 327446.

It is a happy number.

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

It is an interprime number because it is at equal distance from previous prime (644717) and next prime (644729).

It is a cyclic number.

It is not a de Polignac number, because 644723 - 2¹⁸ = 382579 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 644692 and 644701.

It is not an unprimeable number, because it can be changed into a prime (644729) 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, 2015 + ... + 2312.

It is an arithmetic number, because the mean of its divisors is an integer number (162300).

2⁶⁴⁴⁷²³ is an apocalyptic number.

644723 is a deficient number, since it is larger than the sum of its proper divisors (4477).

644723 is a wasteful number, since it uses less digits than its factorization.

644723 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4476.

The product of its digits is 4032, while the sum is 26.

The square root of 644723 is about 802.9464490238. The cubic root of 644723 is about 86.3888556585.

The spelling of 644723 in words is "six hundred forty-four thousand, seven hundred twenty-three".