21005285 has 32 divisors (see below), whose sum is σ = 31249152. Its totient is φ = 13224960.

The previous prime is 21005269. The next prime is 21005291. The reversal of 21005285 is 58250012.

It is not a de Polignac number, because 21005285 - 2⁴ = 21005269 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21005285.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 25175 + ... + 25995.

It is an arithmetic number, because the mean of its divisors is an integer number (976536).

Almost surely, 2^21005285 is an apocalyptic number.

It is an amenable number.

21005285 is a deficient number, since it is larger than the sum of its proper divisors (10243867).

21005285 is a wasteful number, since it uses less digits than its factorization.

21005285 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 893.

The product of its (nonzero) digits is 800, while the sum is 23.

The square root of 21005285 is about 4583.1522994550. The cubic root of 21005285 is about 275.9155600052.

Adding to 21005285 its reverse (58250012), we get a palindrome (79255297).

The spelling of 21005285 in words is "twenty-one million, five thousand, two hundred eighty-five".