21693921 has 16 divisors (see below), whose sum is σ = 31051584. Its totient is φ = 13423104.

The previous prime is 21693911. The next prime is 21693937. The reversal of 21693921 is 12939612.

It is not a de Polignac number, because 21693921 - 2¹⁸ = 21431777 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21693911) 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 15 ways as a sum of consecutive naturals, for example, 810 + ... + 6636.

It is an arithmetic number, because the mean of its divisors is an integer number (1940724).

Almost surely, 2^21693921 is an apocalyptic number.

It is an amenable number.

21693921 is a deficient number, since it is larger than the sum of its proper divisors (9357663).

21693921 is a wasteful number, since it uses less digits than its factorization.

21693921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5920.

The product of its digits is 5832, while the sum is 33.

The square root of 21693921 is about 4657.6733462105. The cubic root of 21693921 is about 278.8983969911.

The spelling of 21693921 in words is "twenty-one million, six hundred ninety-three thousand, nine hundred twenty-one".