21305887 has 4 divisors (see below), whose sum is σ = 21373416. Its totient is φ = 21238360.

The previous prime is 21305857. The next prime is 21305891. The reversal of 21305887 is 78850312.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21305887 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 (21305857) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 33289 + ... + 33922.

It is an arithmetic number, because the mean of its divisors is an integer number (5343354).

Almost surely, 2^21305887 is an apocalyptic number.

21305887 is a deficient number, since it is larger than the sum of its proper divisors (67529).

21305887 is an equidigital number, since it uses as much as digits as its factorization.

21305887 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 67528.

The product of its (nonzero) digits is 13440, while the sum is 34.

The square root of 21305887 is about 4615.8300445315. The cubic root of 21305887 is about 277.2255197928.

The spelling of 21305887 in words is "twenty-one million, three hundred five thousand, eight hundred eighty-seven".