21257321 has 4 divisors (see below), whose sum is σ = 21298644. Its totient is φ = 21216000.

The previous prime is 21257303. The next prime is 21257323. The reversal of 21257321 is 12375212.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 14440000 + 6817321 = 3800^2 + 2611^2 .

It is a cyclic number.

It is not a de Polignac number, because 21257321 - 2²² = 17063017 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21257323) 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, 19880 + ... + 20921.

It is an arithmetic number, because the mean of its divisors is an integer number (5324661).

Almost surely, 2^21257321 is an apocalyptic number.

It is an amenable number.

21257321 is a deficient number, since it is larger than the sum of its proper divisors (41323).

21257321 is an equidigital number, since it uses as much as digits as its factorization.

21257321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 41322.

The product of its digits is 840, while the sum is 23.

The square root of 21257321 is about 4610.5662342059. The cubic root of 21257321 is about 277.0147176860.

The spelling of 21257321 in words is "twenty-one million, two hundred fifty-seven thousand, three hundred twenty-one".