21572399 has 4 divisors (see below), whose sum is σ = 21600264. Its totient is φ = 21544536.

The previous prime is 21572387. The next prime is 21572401. The reversal of 21572399 is 99327512.

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 21572399 - 2²⁴ = 4795183 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 (21572339) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 12737 + ... + 14330.

It is an arithmetic number, because the mean of its divisors is an integer number (5400066).

Almost surely, 2^21572399 is an apocalyptic number.

21572399 is a deficient number, since it is larger than the sum of its proper divisors (27865).

21572399 is an equidigital number, since it uses as much as digits as its factorization.

21572399 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27864.

The product of its digits is 34020, while the sum is 38.

The square root of 21572399 is about 4644.6096714363. The cubic root of 21572399 is about 278.3766567755.

The spelling of 21572399 in words is "twenty-one million, five hundred seventy-two thousand, three hundred ninety-nine".