21521565 has 32 divisors (see below), whose sum is σ = 41207040. Its totient is φ = 10594368.

The previous prime is 21521557. The next prime is 21521579. The reversal of 21521565 is 56512512.

It is not a de Polignac number, because 21521565 - 2³ = 21521557 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent 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 31 ways as a sum of consecutive naturals, for example, 4377 + ... + 7886.

It is an arithmetic number, because the mean of its divisors is an integer number (1287720).

Almost surely, 2^21521565 is an apocalyptic number.

It is an amenable number.

21521565 is a deficient number, since it is larger than the sum of its proper divisors (19685475).

21521565 is a wasteful number, since it uses less digits than its factorization.

21521565 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12290 (or 12284 counting only the distinct ones).

The product of its digits is 3000, while the sum is 27.

The square root of 21521565 is about 4639.1340786832. The cubic root of 21521565 is about 278.1578257767.

The spelling of 21521565 in words is "twenty-one million, five hundred twenty-one thousand, five hundred sixty-five".