21257999 has 4 divisors (see below), whose sum is σ = 24294864. Its totient is φ = 18221136.

The previous prime is 21257993. The next prime is 21258001. The reversal of 21257999 is 99975212.

It is a happy number.

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 21257999 - 2²⁴ = 4480783 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 (21257993) 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, 1518422 + ... + 1518435.

It is an arithmetic number, because the mean of its divisors is an integer number (6073716).

Almost surely, 2^21257999 is an apocalyptic number.

21257999 is a deficient number, since it is larger than the sum of its proper divisors (3036865).

21257999 is an equidigital number, since it uses as much as digits as its factorization.

21257999 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3036864.

The product of its digits is 102060, while the sum is 44.

The square root of 21257999 is about 4610.6397603803. The cubic root of 21257999 is about 277.0176627731.

The spelling of 21257999 in words is "twenty-one million, two hundred fifty-seven thousand, nine hundred ninety-nine".