21686920 has 32 divisors (see below), whose sum is σ = 48942720. Its totient is φ = 8648640.

The previous prime is 21686891. The next prime is 21686927. The reversal of 21686920 is 2968612.

It is a happy number.

It is a Smith number, since the sum of its digits (34) coincides with the sum of the digits of its prime factors.

It is not an unprimeable number, because it can be changed into a prime (21686927) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 17935 + ... + 19105.

It is an arithmetic number, because the mean of its divisors is an integer number (1529460).

Almost surely, 2^21686920 is an apocalyptic number.

21686920 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21686920 is an abundant number, since it is smaller than the sum of its proper divisors (27255800).

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

21686920 is a wasteful number, since it uses less digits than its factorization.

21686920 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1645 (or 1641 counting only the distinct ones).

The product of its (nonzero) digits is 10368, while the sum is 34.

The square root of 21686920 is about 4656.9217300702. The cubic root of 21686920 is about 278.8683919994.

The spelling of 21686920 in words is "twenty-one million, six hundred eighty-six thousand, nine hundred twenty".