644890 has 8 divisors (see below), whose sum is σ = 1160820. Its totient is φ = 257952.

The previous prime is 644881. The next prime is 644899. The reversal of 644890 is 98446.

It is an interprime number because it is at equal distance from previous prime (644881) and next prime (644899).

It can be written as a sum of positive squares in 2 ways, for example, as 644809 + 81 = 803^2 + 9^2 .

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

It is a super-2 number, since 2×644890² = 831766224200, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (644899) 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, 32235 + ... + 32254.

2⁶⁴⁴⁸⁹⁰ is an apocalyptic number.

644890 is a deficient number, since it is larger than the sum of its proper divisors (515930).

644890 is a wasteful number, since it uses less digits than its factorization.

644890 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 64496.

The product of its (nonzero) digits is 6912, while the sum is 31.

The square root of 644890 is about 803.0504342817. The cubic root of 644890 is about 86.3963140003.

The spelling of 644890 in words is "six hundred forty-four thousand, eight hundred ninety".