21855636 has 48 divisors (see below), whose sum is σ = 61817280. Its totient is φ = 6622560.

The previous prime is 21855623. The next prime is 21855649. The reversal of 21855636 is 63655812.

21855636 is a `hidden beast` number, since 2 + 18 + 5 + 5 + 636 = 666.

It is an interprime number because it is at equal distance from previous prime (21855623) and next prime (21855649).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a self number, because there is not a number n which added to its sum of digits gives 21855636.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 8011 + ... + 10386.

It is an arithmetic number, because the mean of its divisors is an integer number (1287860).

Almost surely, 2^21855636 is an apocalyptic number.

It is an amenable number.

21855636 is an abundant number, since it is smaller than the sum of its proper divisors (39961644).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21855636 is a wasteful number, since it uses less digits than its factorization.

21855636 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18421 (or 18413 counting only the distinct ones).

The product of its digits is 43200, while the sum is 36.

The square root of 21855636 is about 4675.0011764704. The cubic root of 21855636 is about 279.5896881385.

The spelling of 21855636 in words is "twenty-one million, eight hundred fifty-five thousand, six hundred thirty-six".