21688218 has 24 divisors (see below), whose sum is σ = 49035168. Its totient is φ = 6914952.

The previous prime is 21688217. The next prime is 21688237. The reversal of 21688218 is 81288612.

It is not an unprimeable number, because it can be changed into a prime (21688213) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 25780 + ... + 26607.

It is an arithmetic number, because the mean of its divisors is an integer number (2043132).

Almost surely, 2^21688218 is an apocalyptic number.

21688218 is an abundant number, since it is smaller than the sum of its proper divisors (27346950).

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

21688218 is a wasteful number, since it uses less digits than its factorization.

21688218 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 52418 (or 52415 counting only the distinct ones).

The product of its digits is 12288, while the sum is 36.

The square root of 21688218 is about 4657.0610904303. The cubic root of 21688218 is about 278.8739554750.

The spelling of 21688218 in words is "twenty-one million, six hundred eighty-eight thousand, two hundred eighteen".