21057259 has 4 divisors (see below), whose sum is σ = 21972816. Its totient is φ = 20141704.

The previous prime is 21057247. The next prime is 21057287. The reversal of 21057259 is 95275012.

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 21057259 - 2⁷ = 21057131 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21057259.

It is not an unprimeable number, because it can be changed into a prime (21057209) 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, 457744 + ... + 457789.

It is an arithmetic number, because the mean of its divisors is an integer number (5493204).

Almost surely, 2^21057259 is an apocalyptic number.

21057259 is a deficient number, since it is larger than the sum of its proper divisors (915557).

21057259 is an equidigital number, since it uses as much as digits as its factorization.

21057259 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 915556.

The product of its (nonzero) digits is 6300, while the sum is 31.

The square root of 21057259 is about 4588.8189112232. The cubic root of 21057259 is about 276.1429412554.

It can be divided in two parts, 21057 and 259, that added together give a square (21316 = 146²).

The spelling of 21057259 in words is "twenty-one million, fifty-seven thousand, two hundred fifty-nine".