21393523 has 4 divisors (see below), whose sum is σ = 21458488. Its totient is φ = 21328560.

The previous prime is 21393521. The next prime is 21393551. The reversal of 21393523 is 32539312.

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 21393523 - 2¹ = 21393521 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21393491 and 21393500.

It is not an unprimeable number, because it can be changed into a prime (21393521) 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, 31986 + ... + 32647.

It is an arithmetic number, because the mean of its divisors is an integer number (5364622).

Almost surely, 2^21393523 is an apocalyptic number.

21393523 is a deficient number, since it is larger than the sum of its proper divisors (64965).

21393523 is an equidigital number, since it uses as much as digits as its factorization.

21393523 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 64964.

The product of its digits is 4860, while the sum is 28.

The square root of 21393523 is about 4625.3132866866. The cubic root of 21393523 is about 277.6050972206.

The spelling of 21393523 in words is "twenty-one million, three hundred ninety-three thousand, five hundred twenty-three".