21668736 has 64 divisors (see below), whose sum is σ = 58421520. Its totient is φ = 7114752.

The previous prime is 21668729. The next prime is 21668743. The reversal of 21668736 is 63786612.

It is an interprime number because it is at equal distance from previous prime (21668729) and next prime (21668743).

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

It is a junction number, because it is equal to n+sod(n) for n = 21668694 and 21668703.

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, 27646 + ... + 28418.

Almost surely, 2^21668736 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 21668736, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29210760).

21668736 is an abundant number, since it is smaller than the sum of its proper divisors (36752784).

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

21668736 is an equidigital number, since it uses as much as digits as its factorization.

21668736 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 863 (or 851 counting only the distinct ones).

The product of its digits is 72576, while the sum is 39.

The square root of 21668736 is about 4654.9689580061. The cubic root of 21668736 is about 278.7904285574.

The spelling of 21668736 in words is "twenty-one million, six hundred sixty-eight thousand, seven hundred thirty-six".