21573215 has 4 divisors (see below), whose sum is σ = 25887864. Its totient is φ = 17258568.

The previous prime is 21573203. The next prime is 21573239. The reversal of 21573215 is 51237512.

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 21573215 - 2¹⁸ = 21311071 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2157317 + ... + 2157326.

It is an arithmetic number, because the mean of its divisors is an integer number (6471966).

Almost surely, 2^21573215 is an apocalyptic number.

21573215 is a deficient number, since it is larger than the sum of its proper divisors (4314649).

21573215 is an equidigital number, since it uses as much as digits as its factorization.

21573215 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4314648.

The product of its digits is 2100, while the sum is 26.

The square root of 21573215 is about 4644.6975143706. The cubic root of 21573215 is about 278.3801667002.

The spelling of 21573215 in words is "twenty-one million, five hundred seventy-three thousand, two hundred fifteen".