21520539 has 8 divisors (see below), whose sum is σ = 31882320. Its totient is φ = 14347008.

The previous prime is 21520537. The next prime is 21520547. The reversal of 21520539 is 93502512.

It is not a de Polignac number, because 21520539 - 2¹ = 21520537 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27), and also a Moran number because the ratio is a prime number: 797057 = 21520539 / (2 + 1 + 5 + 2 + 0 + 5 + 3 + 9).

It is not an unprimeable number, because it can be changed into a prime (21520537) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 398502 + ... + 398555.

It is an arithmetic number, because the mean of its divisors is an integer number (3985290).

Almost surely, 2^21520539 is an apocalyptic number.

21520539 is a deficient number, since it is larger than the sum of its proper divisors (10361781).

21520539 is an equidigital number, since it uses as much as digits as its factorization.

21520539 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 797066 (or 797060 counting only the distinct ones).

The product of its (nonzero) digits is 2700, while the sum is 27.

The square root of 21520539 is about 4639.0234963837. The cubic root of 21520539 is about 278.1534054900.

The spelling of 21520539 in words is "twenty-one million, five hundred twenty thousand, five hundred thirty-nine".