21388565 has 12 divisors (see below), whose sum is σ = 28212492. Its totient is φ = 15554880.

The previous prime is 21388559. The next prime is 21388583. The reversal of 21388565 is 56588312.

It can be written as a sum of positive squares in 2 ways, for example, as 16834609 + 4553956 = 4103^2 + 2134^2 .

It is not a de Polignac number, because 21388565 - 2¹⁴ = 21372181 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 17072 + ... + 18281.

It is an arithmetic number, because the mean of its divisors is an integer number (2351041).

Almost surely, 2^21388565 is an apocalyptic number.

It is an amenable number.

21388565 is a deficient number, since it is larger than the sum of its proper divisors (6823927).

21388565 is a wasteful number, since it uses less digits than its factorization.

21388565 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 35380 (or 35369 counting only the distinct ones).

The product of its digits is 57600, while the sum is 38.

The square root of 21388565 is about 4624.7772919353. Note that the first 3 decimals coincide. The cubic root of 21388565 is about 277.5836503491.

The spelling of 21388565 in words is "twenty-one million, three hundred eighty-eight thousand, five hundred sixty-five".