644536 has 8 divisors (see below), whose sum is σ = 1208520. Its totient is φ = 322264.

The previous prime is 644531. The next prime is 644549. The reversal of 644536 is 635446.

It is a tau number, because it is divible by the number of its divisors (8).

It is a hoax number, since the sum of its digits (28) coincides with the sum of the digits of its distinct prime factors.

It is a d-powerful number, because it can be written as 6⁷ + 4⁴ + 5⁷ + 4⁶ + 3⁷ + 6⁷ .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644531) 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 as a sum of consecutive naturals, namely, 40276 + ... + 40291.

It is an arithmetic number, because the mean of its divisors is an integer number (151065).

2⁶⁴⁴⁵³⁶ is an apocalyptic number.

It is an amenable number.

644536 is a deficient number, since it is larger than the sum of its proper divisors (563984).

644536 is a wasteful number, since it uses less digits than its factorization.

644536 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 80573 (or 80569 counting only the distinct ones).

The product of its digits is 8640, while the sum is 28.

The square root of 644536 is about 802.8299944571. The cubic root of 644536 is about 86.3805025735.

The spelling of 644536 in words is "six hundred forty-four thousand, five hundred thirty-six".