21388355 has 4 divisors (see below), whose sum is σ = 25666032. Its totient is φ = 17110680.

The previous prime is 21388333. The next prime is 21388373. The reversal of 21388355 is 55388312.

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

It is not a de Polignac number, because 21388355 - 2⁸ = 21388099 is a prime.

It is a Duffinian number.

It is an unprimeable number.

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, 2138831 + ... + 2138840.

It is an arithmetic number, because the mean of its divisors is an integer number (6416508).

Almost surely, 2^21388355 is an apocalyptic number.

21388355 is a deficient number, since it is larger than the sum of its proper divisors (4277677).

21388355 is an equidigital number, since it uses as much as digits as its factorization.

21388355 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4277676.

The product of its digits is 28800, while the sum is 35.

The square root of 21388355 is about 4624.7545880836. The cubic root of 21388355 is about 277.5827418768.

The spelling of 21388355 in words is "twenty-one million, three hundred eighty-eight thousand, three hundred fifty-five".