21666688 has 64 divisors (see below), whose sum is σ = 46512000. Its totient is φ = 10022400.

The previous prime is 21666679. The next prime is 21666691. The reversal of 21666688 is 88666612.

It is a tau number, because it is divible by the number of its divisors (64).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 143413 + ... + 143563.

It is an arithmetic number, because the mean of its divisors is an integer number (726750).

Almost surely, 2^21666688 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21666688, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23256000).

21666688 is an abundant number, since it is smaller than the sum of its proper divisors (24845312).

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

21666688 is a wasteful number, since it uses less digits than its factorization.

21666688 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 243 (or 231 counting only the distinct ones).

The product of its digits is 165888, while the sum is 43.

The square root of 21666688 is about 4654.7489728233. The cubic root of 21666688 is about 278.7816450765.

The spelling of 21666688 in words is "twenty-one million, six hundred sixty-six thousand, six hundred eighty-eight".