21388857 has 32 divisors (see below), whose sum is σ = 33807360. Its totient is φ = 11776320.

The previous prime is 21388837. The next prime is 21388867. The reversal of 21388857 is 75888312.

It is a happy number.

It is not a de Polignac number, because 21388857 - 2¹⁰ = 21387833 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21388837) 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 31 ways as a sum of consecutive naturals, for example, 75438 + ... + 75720.

It is an arithmetic number, because the mean of its divisors is an integer number (1056480).

Almost surely, 2^21388857 is an apocalyptic number.

It is an amenable number.

21388857 is a deficient number, since it is larger than the sum of its proper divisors (12418503).

21388857 is a wasteful number, since it uses less digits than its factorization.

21388857 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 413.

The product of its digits is 107520, while the sum is 42.

The square root of 21388857 is about 4624.8088609152. The cubic root of 21388857 is about 277.5849135484.

The spelling of 21388857 in words is "twenty-one million, three hundred eighty-eight thousand, eight hundred fifty-seven".