644813 has 8 divisors (see below), whose sum is σ = 700728. Its totient is φ = 589824.

The previous prime is 644801. The next prime is 644837. The reversal of 644813 is 318446.

It can be written as a sum of positive squares in 4 ways, for example, as 94249 + 550564 = 307^2 + 742^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 644813 - 2⁴ = 644797 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 644813.

It is not an unprimeable number, because it can be changed into a prime (644843) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2381 + ... + 2637.

It is an arithmetic number, because the mean of its divisors is an integer number (87591).

2⁶⁴⁴⁸¹³ is an apocalyptic number.

It is an amenable number.

644813 is a deficient number, since it is larger than the sum of its proper divisors (55915).

644813 is a wasteful number, since it uses less digits than its factorization.

644813 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 463.

The product of its digits is 2304, while the sum is 26.

The square root of 644813 is about 803.0024906562. The cubic root of 644813 is about 86.3928752841.

The spelling of 644813 in words is "six hundred forty-four thousand, eight hundred thirteen".