644866 has 4 divisors (see below), whose sum is σ = 967302. Its totient is φ = 322432.

The previous prime is 644863. The next prime is 644867. The reversal of 644866 is 668446.

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., 606841 + 38025 = 779^2 + 195^2 .

It is a nialpdrome in base 15.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644863) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 161215 + ... + 161218.

2⁶⁴⁴⁸⁶⁶ is an apocalyptic number.

644866 is a deficient number, since it is larger than the sum of its proper divisors (322436).

644866 is a wasteful number, since it uses less digits than its factorization.

644866 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 322435.

The product of its digits is 27648, while the sum is 34.

The square root of 644866 is about 803.0354911210. The cubic root of 644866 is about 86.3952422220.

The spelling of 644866 in words is "six hundred forty-four thousand, eight hundred sixty-six".