21388369 has 4 divisors (see below), whose sum is σ = 21739060. Its totient is φ = 21037680.

The previous prime is 21388333. The next prime is 21388373. The reversal of 21388369 is 96388312.

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

It can be written as a sum of positive squares in 2 ways, for example, as 3283344 + 18105025 = 1812^2 + 4255^2 .

It is not a de Polignac number, because 21388369 - 2¹⁷ = 21257297 is a prime.

It is a super-2 number, since 2×21388369² = 914924656960322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21388469) by changing a digit.

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, 175254 + ... + 175375.

It is an arithmetic number, because the mean of its divisors is an integer number (5434765).

Almost surely, 2^21388369 is an apocalyptic number.

It is an amenable number.

21388369 is a deficient number, since it is larger than the sum of its proper divisors (350691).

21388369 is an equidigital number, since it uses as much as digits as its factorization.

21388369 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 350690.

The product of its digits is 62208, while the sum is 40.

The square root of 21388369 is about 4624.7561016771. The cubic root of 21388369 is about 277.5828024418.

The spelling of 21388369 in words is "twenty-one million, three hundred eighty-eight thousand, three hundred sixty-nine".