21538573 has 4 divisors (see below), whose sum is σ = 24615520. Its totient is φ = 18461628.

The previous prime is 21538567. The next prime is 21538579. The reversal of 21538573 is 37583512.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is an interprime number because it is at equal distance from previous prime (21538567) and next prime (21538579).

It is a cyclic number.

It is not a de Polignac number, because 21538573 - 2⁹ = 21538061 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21538579) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1538463 + ... + 1538476.

It is an arithmetic number, because the mean of its divisors is an integer number (6153880).

Almost surely, 2^21538573 is an apocalyptic number.

It is an amenable number.

21538573 is a deficient number, since it is larger than the sum of its proper divisors (3076947).

21538573 is an equidigital number, since it uses as much as digits as its factorization.

21538573 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3076946.

The product of its digits is 25200, while the sum is 34.

The square root of 21538573 is about 4640.9668173776. The cubic root of 21538573 is about 278.2310804030.

The spelling of 21538573 in words is "twenty-one million, five hundred thirty-eight thousand, five hundred seventy-three".