21594721 has 4 divisors (see below), whose sum is σ = 21898944. Its totient is φ = 21290500.

The previous prime is 21594707. The next prime is 21594731. The reversal of 21594721 is 12749512.

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 21594721 - 2¹⁷ = 21463649 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21594701) 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, 152005 + ... + 152146.

It is an arithmetic number, because the mean of its divisors is an integer number (5474736).

Almost surely, 2^21594721 is an apocalyptic number.

It is an amenable number.

21594721 is a deficient number, since it is larger than the sum of its proper divisors (304223).

21594721 is an equidigital number, since it uses as much as digits as its factorization.

21594721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 304222.

The product of its digits is 5040, while the sum is 31.

The square root of 21594721 is about 4647.0120507698. The cubic root of 21594721 is about 278.4726402539.

The spelling of 21594721 in words is "twenty-one million, five hundred ninety-four thousand, seven hundred twenty-one".