21684887 has 4 divisors (see below), whose sum is σ = 24782736. Its totient is φ = 18587040.

The previous prime is 21684881. The next prime is 21684893. The reversal of 21684887 is 78848612.

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

It is an interprime number because it is at equal distance from previous prime (21684881) and next prime (21684893).

It is a cyclic number.

It is not a de Polignac number, because 21684887 - 2¹⁸ = 21422743 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 (21684881) 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, 1548914 + ... + 1548927.

It is an arithmetic number, because the mean of its divisors is an integer number (6195684).

Almost surely, 2^21684887 is an apocalyptic number.

21684887 is a deficient number, since it is larger than the sum of its proper divisors (3097849).

21684887 is an equidigital number, since it uses as much as digits as its factorization.

21684887 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3097848.

The product of its digits is 172032, while the sum is 44.

The square root of 21684887 is about 4656.7034477192. The cubic root of 21684887 is about 278.8596777275.

The spelling of 21684887 in words is "twenty-one million, six hundred eighty-four thousand, eight hundred eighty-seven".