21187845 has 48 divisors (see below), whose sum is σ = 43830720. Its totient is φ = 9682848.

The previous prime is 21187843. The next prime is 21187847. The reversal of 21187845 is 54878112.

It is an interprime number because it is at equal distance from previous prime (21187843) and next prime (21187847).

It is not a de Polignac number, because 21187845 - 2¹ = 21187843 is a prime.

It is a Smith number, since the sum of its digits (36) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21187843) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 5014 + ... + 8216.

It is an arithmetic number, because the mean of its divisors is an integer number (913140).

Almost surely, 2^21187845 is an apocalyptic number.

It is an amenable number.

21187845 is an abundant number, since it is smaller than the sum of its proper divisors (22642875).

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

21187845 is a wasteful number, since it uses less digits than its factorization.

21187845 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3231 (or 3218 counting only the distinct ones).

The product of its digits is 17920, while the sum is 36.

The square root of 21187845 is about 4603.0256353838. The cubic root of 21187845 is about 276.7125962038.

The spelling of 21187845 in words is "twenty-one million, one hundred eighty-seven thousand, eight hundred forty-five".