21684906 has 24 divisors (see below), whose sum is σ = 49027680. Its totient is φ = 6913896.

The previous prime is 21684893. The next prime is 21684913. The reversal of 21684906 is 60948612.

21684906 is a `hidden beast` number, since 2 + 168 + 490 + 6 = 666.

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

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 25776 + ... + 26603.

It is an arithmetic number, because the mean of its divisors is an integer number (2042820).

Almost surely, 2^21684906 is an apocalyptic number.

21684906 is an abundant number, since it is smaller than the sum of its proper divisors (27342774).

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

21684906 is a wasteful number, since it uses less digits than its factorization.

21684906 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 52410 (or 52407 counting only the distinct ones).

The product of its (nonzero) digits is 20736, while the sum is 36.

The square root of 21684906 is about 4656.7054877886. The cubic root of 21684906 is about 278.8597591718.

The spelling of 21684906 in words is "twenty-one million, six hundred eighty-four thousand, nine hundred six".