21361664 has 44 divisors (see below), whose sum is σ = 44608224. Its totient is φ = 10205184.

The previous prime is 21361619. The next prime is 21361709. The reversal of 21361664 is 46616312.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21361619) and next prime (21361709).

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, 23099 + ... + 24005.

Almost surely, 2^21361664 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 21361664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22304112).

21361664 is an abundant number, since it is smaller than the sum of its proper divisors (23246560).

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

21361664 is an equidigital number, since it uses as much as digits as its factorization.

21361664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 950 (or 932 counting only the distinct ones).

The product of its digits is 5184, while the sum is 29.

The square root of 21361664 is about 4621.8680206168. The cubic root of 21361664 is about 277.4672266033.

Adding to 21361664 its reverse (46616312), we get a palindrome (67977976).

The spelling of 21361664 in words is "twenty-one million, three hundred sixty-one thousand, six hundred sixty-four".