21706664 has 64 divisors (see below), whose sum is σ = 51148800. Its totient is φ = 8420544.

The previous prime is 21706639. The next prime is 21706693. The reversal of 21706664 is 46660712.

It is a self number, because there is not a number n which added to its sum of digits gives 21706664.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 24029 + ... + 24915.

It is an arithmetic number, because the mean of its divisors is an integer number (799200).

Almost surely, 2^21706664 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 21706664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25574400).

21706664 is an abundant number, since it is smaller than the sum of its proper divisors (29442136).

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

21706664 is a wasteful number, since it uses less digits than its factorization.

21706664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 942 (or 938 counting only the distinct ones).

The product of its (nonzero) digits is 12096, while the sum is 32.

The square root of 21706664 is about 4659.0411030597. The cubic root of 21706664 is about 278.9529945690.

The spelling of 21706664 in words is "twenty-one million, seven hundred six thousand, six hundred sixty-four".