639533521 has 21 divisors (see below), whose sum is σ = 742461177. Its totient is φ = 550794420.

The previous prime is 639533459. The next prime is 639533537. The reversal of 639533521 is 125335936.

The square root of 639533521 is 25289.

It is a perfect power (a square), and thus also a powerful number.

It is not a de Polignac number, because 639533521 - 2²⁷ = 505315793 is a prime.

It is a Duffinian number.

Its product of digits (72900) is a multiple of the sum of its prime divisors (30).

It is not an unprimeable number, because it can be changed into a prime (639533551) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 20 ways as a sum of consecutive naturals, for example, 33659650 + ... + 33659668.

Almost surely, 2^639533521 is an apocalyptic number.

639533521 is the 25289-th square number.

639533521 is the 12645-th centered octagonal number.

It is an amenable number.

639533521 is a deficient number, since it is larger than the sum of its proper divisors (102927656).

639533521 is an frugal number, since it uses more digits than its factorization.

639533521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 104 (or 30 counting only the distinct ones).

The product of its digits is 72900, while the sum is 37.

The cubic root of 639533521 is about 861.5644504271.

Multiplying 639533521 by its product of digits (72900), we get a square (46621993680900 = 6828030²).

The spelling of 639533521 in words is "six hundred thirty-nine million, five hundred thirty-three thousand, five hundred twenty-one".