21057397 has 4 divisors (see below), whose sum is σ = 21972960. Its totient is φ = 20141836.

The previous prime is 21057341. The next prime is 21057419. The reversal of 21057397 is 79375012.

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 not a de Polignac number, because 21057397 - 2¹⁵ = 21024629 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 (21057307) 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, 457747 + ... + 457792.

It is an arithmetic number, because the mean of its divisors is an integer number (5493240).

Almost surely, 2^21057397 is an apocalyptic number.

It is an amenable number.

21057397 is a deficient number, since it is larger than the sum of its proper divisors (915563).

21057397 is an equidigital number, since it uses as much as digits as its factorization.

21057397 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 915562.

The product of its (nonzero) digits is 13230, while the sum is 34.

The square root of 21057397 is about 4588.8339477475. The cubic root of 21057397 is about 276.1435444938.

The spelling of 21057397 in words is "twenty-one million, fifty-seven thousand, three hundred ninety-seven".