644668 has 6 divisors (see below), whose sum is σ = 1128176. Its totient is φ = 322332.

The previous prime is 644653. The next prime is 644669. The reversal of 644668 is 866446.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644669) by changing a digit.

644668 is an untouchable number, because it is not equal to the sum of proper divisors of any 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, 80580 + ... + 80587.

2⁶⁴⁴⁶⁶⁸ is an apocalyptic number.

It is an amenable number.

644668 is a deficient number, since it is larger than the sum of its proper divisors (483508).

644668 is a wasteful number, since it uses less digits than its factorization.

644668 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 161171 (or 161169 counting only the distinct ones).

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

The square root of 644668 is about 802.9121994340. The cubic root of 644668 is about 86.3863990365.

The spelling of 644668 in words is "six hundred forty-four thousand, six hundred sixty-eight".