21185887 has 4 divisors (see below), whose sum is σ = 21195216. Its totient is φ = 21176560.

The previous prime is 21185881. The next prime is 21185891. The reversal of 21185887 is 78858112.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21185887 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 (21185881) 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, 1203 + ... + 6619.

It is an arithmetic number, because the mean of its divisors is an integer number (5298804).

Almost surely, 2^21185887 is an apocalyptic number.

21185887 is a deficient number, since it is larger than the sum of its proper divisors (9329).

21185887 is an equidigital number, since it uses as much as digits as its factorization.

21185887 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9328.

The product of its digits is 35840, while the sum is 40.

The square root of 21185887 is about 4602.8129442766. The cubic root of 21185887 is about 276.7040721348.

The spelling of 21185887 in words is "twenty-one million, one hundred eighty-five thousand, eight hundred eighty-seven".