21539645 has 8 divisors (see below), whose sum is σ = 25885656. Its totient is φ = 17206336.

The previous prime is 21539621. The next prime is 21539653. The reversal of 21539645 is 54693512.

It can be written as a sum of positive squares in 4 ways, for example, as 1136356 + 20403289 = 1066^2 + 4517^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 21539645 - 2¹⁴ = 21523261 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

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 7 ways as a sum of consecutive naturals, for example, 1079 + ... + 6651.

It is an arithmetic number, because the mean of its divisors is an integer number (3235707).

Almost surely, 2^21539645 is an apocalyptic number.

It is an amenable number.

21539645 is a deficient number, since it is larger than the sum of its proper divisors (4346011).

21539645 is an equidigital number, since it uses as much as digits as its factorization.

21539645 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6351.

The product of its digits is 32400, while the sum is 35.

The square root of 21539645 is about 4641.0823091171. The cubic root of 21539645 is about 278.2356962887.

The spelling of 21539645 in words is "twenty-one million, five hundred thirty-nine thousand, six hundred forty-five".