644818 has 4 divisors (see below), whose sum is σ = 967230. Its totient is φ = 322408.

The previous prime is 644801. The next prime is 644837. The reversal of 644818 is 818446.

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

It can be written as a sum of positive squares in only one way, i.e., 644809 + 9 = 803^2 + 3^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 644818.

It is an unprimeable number.

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 as a sum of consecutive naturals, namely, 161203 + ... + 161206.

2⁶⁴⁴⁸¹⁸ is an apocalyptic number.

644818 is a deficient number, since it is larger than the sum of its proper divisors (322412).

644818 is a wasteful number, since it uses less digits than its factorization.

644818 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 322411.

The product of its digits is 6144, while the sum is 31.

The square root of 644818 is about 803.0056039655. The cubic root of 644818 is about 86.3930985857.

The spelling of 644818 in words is "six hundred forty-four thousand, eight hundred eighteen".