21668416 has 56 divisors (see below), whose sum is σ = 53620416. Its totient is φ = 8440320.

The previous prime is 21668401. The next prime is 21668429. The reversal of 21668416 is 61486612.

It is a tau number, because it is divible by the number of its divisors (56).

It is a hoax number, since the sum of its digits (34) coincides with the sum of the digits of its distinct prime factors.

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, 2730 + ... + 7126.

Almost surely, 2^21668416 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 21668416, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26810208).

21668416 is an abundant number, since it is smaller than the sum of its proper divisors (31952000).

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

21668416 is a wasteful number, since it uses less digits than its factorization.

21668416 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4427 (or 4417 counting only the distinct ones).

The product of its digits is 13824, while the sum is 34.

The square root of 21668416 is about 4654.9345860066. The cubic root of 21668416 is about 278.7890561750.

The spelling of 21668416 in words is "twenty-one million, six hundred sixty-eight thousand, four hundred sixteen".