21545539 has 4 divisors (see below), whose sum is σ = 21613824. Its totient is φ = 21477256.

The previous prime is 21545509. The next prime is 21545551. The reversal of 21545539 is 93554512.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21545539 - 2¹⁹ = 21021251 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21545509) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 33667 + ... + 34300.

It is an arithmetic number, because the mean of its divisors is an integer number (5403456).

Almost surely, 2^21545539 is an apocalyptic number.

21545539 is a deficient number, since it is larger than the sum of its proper divisors (68285).

21545539 is an equidigital number, since it uses as much as digits as its factorization.

21545539 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 68284.

The product of its digits is 27000, while the sum is 34.

The square root of 21545539 is about 4641.7172468818. The cubic root of 21545539 is about 278.2610723125.

It can be divided in two parts, 215 and 45539, that added together give a palindrome (45754).

The spelling of 21545539 in words is "twenty-one million, five hundred forty-five thousand, five hundred thirty-nine".