21688385 has 16 divisors (see below), whose sum is σ = 27240192. Its totient is φ = 16560000.

The previous prime is 21688343. The next prime is 21688391. The reversal of 21688385 is 58388612.

It is not a de Polignac number, because 21688385 - 2¹⁰ = 21687361 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (41).

It is a Duffinian number.

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 8510 + ... + 10760.

It is an arithmetic number, because the mean of its divisors is an integer number (1702512).

Almost surely, 2^21688385 is an apocalyptic number.

It is an amenable number.

21688385 is a deficient number, since it is larger than the sum of its proper divisors (5551807).

21688385 is a wasteful number, since it uses less digits than its factorization.

21688385 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2344.

The product of its digits is 92160, while the sum is 41.

The square root of 21688385 is about 4657.0790201585. The cubic root of 21688385 is about 278.8746712528.

The spelling of 21688385 in words is "twenty-one million, six hundred eighty-eight thousand, three hundred eighty-five".