21393664 has 36 divisors (see below), whose sum is σ = 43024156. Its totient is φ = 10616832.

The previous prime is 21393653. The next prime is 21393683. The reversal of 21393664 is 46639312.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 3686400 + 17707264 = 1920^2 + 4208^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 49192 + ... + 49624.

Almost surely, 2^21393664 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 21393664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (21512078).

21393664 is an abundant number, since it is smaller than the sum of its proper divisors (21630492).

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

21393664 is an equidigital number, since it uses as much as digits as its factorization.

21393664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 642 (or 628 counting only the distinct ones).

The product of its digits is 23328, while the sum is 34.

The square root of 21393664 is about 4625.3285288723. The cubic root of 21393664 is about 277.6057070972.

The spelling of 21393664 in words is "twenty-one million, three hundred ninety-three thousand, six hundred sixty-four".