21684871 has 8 divisors (see below), whose sum is σ = 24582320. Its totient is φ = 18963072.

The previous prime is 21684863. The next prime is 21684881. The reversal of 21684871 is 17848612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21684871 - 2³ = 21684863 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21684871.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21684811) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 43650 + ... + 44143.

It is an arithmetic number, because the mean of its divisors is an integer number (3072790).

Almost surely, 2^21684871 is an apocalyptic number.

21684871 is a deficient number, since it is larger than the sum of its proper divisors (2897449).

21684871 is a wasteful number, since it uses less digits than its factorization.

21684871 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 87825.

The product of its digits is 21504, while the sum is 37.

The square root of 21684871 is about 4656.7017297654. The cubic root of 21684871 is about 278.8596091427.

The spelling of 21684871 in words is "twenty-one million, six hundred eighty-four thousand, eight hundred seventy-one".