21645559 has 4 divisors (see below), whose sum is σ = 23310616. Its totient is φ = 19980504.

The previous prime is 21645551. The next prime is 21645619. The reversal of 21645559 is 95554612.

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

It is a cyclic number.

It is not a de Polignac number, because 21645559 - 2³ = 21645551 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 (21645551) 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, 832509 + ... + 832534.

It is an arithmetic number, because the mean of its divisors is an integer number (5827654).

Almost surely, 2^21645559 is an apocalyptic number.

21645559 is a deficient number, since it is larger than the sum of its proper divisors (1665057).

21645559 is a wasteful number, since it uses less digits than its factorization.

21645559 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1665056.

The product of its digits is 54000, while the sum is 37.

The square root of 21645559 is about 4652.4788016712. The cubic root of 21645559 is about 278.6909945019.

The spelling of 21645559 in words is "twenty-one million, six hundred forty-five thousand, five hundred fifty-nine".