21573537 has 4 divisors (see below), whose sum is σ = 28764720. Its totient is φ = 14382356.

The previous prime is 21573533. The next prime is 21573547. The reversal of 21573537 is 73537512.

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 a cyclic number.

It is not a de Polignac number, because 21573537 - 2² = 21573533 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21573498 and 21573507.

It is not an unprimeable number, because it can be changed into a prime (21573533) 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, 3595587 + ... + 3595592.

It is an arithmetic number, because the mean of its divisors is an integer number (7191180).

Almost surely, 2^21573537 is an apocalyptic number.

It is an amenable number.

21573537 is a deficient number, since it is larger than the sum of its proper divisors (7191183).

21573537 is an equidigital number, since it uses as much as digits as its factorization.

21573537 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7191182.

The product of its digits is 22050, while the sum is 33.

The square root of 21573537 is about 4644.7321774242. The cubic root of 21573537 is about 278.3815517196.

The spelling of 21573537 in words is "twenty-one million, five hundred seventy-three thousand, five hundred thirty-seven".