21388397 has 4 divisors (see below), whose sum is σ = 22646556. Its totient is φ = 20130240.

The previous prime is 21388373. The next prime is 21388417. The reversal of 21388397 is 79388312.

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 14280841 + 7107556 = 3779^2 + 2666^2 .

It is a cyclic number.

It is not a de Polignac number, because 21388397 - 2⁶ = 21388333 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 (21388327) 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, 629054 + ... + 629087.

It is an arithmetic number, because the mean of its divisors is an integer number (5661639).

Almost surely, 2^21388397 is an apocalyptic number.

It is an amenable number.

21388397 is a deficient number, since it is larger than the sum of its proper divisors (1258159).

21388397 is a wasteful number, since it uses less digits than its factorization.

21388397 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1258158.

The product of its digits is 72576, while the sum is 41.

The square root of 21388397 is about 4624.7591288628. The cubic root of 21388397 is about 277.5829235718.

The spelling of 21388397 in words is "twenty-one million, three hundred eighty-eight thousand, three hundred ninety-seven".