21216764 has 24 divisors (see below), whose sum is σ = 39137280. Its totient is φ = 10044144.

The previous prime is 21216751. The next prime is 21216773. The reversal of 21216764 is 46761212.

It is a Smith number, since the sum of its digits (29) coincides with the sum of the digits of its prime factors.

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, 8357 + ... + 10595.

It is an arithmetic number, because the mean of its divisors is an integer number (1630720).

Almost surely, 2^21216764 is an apocalyptic number.

It is an amenable number.

21216764 is a deficient number, since it is larger than the sum of its proper divisors (17920516).

21216764 is a wasteful number, since it uses less digits than its factorization.

21216764 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2369 (or 2367 counting only the distinct ones).

The product of its digits is 4032, while the sum is 29.

The square root of 21216764 is about 4606.1658676170. The cubic root of 21216764 is about 276.8384327169.

Adding to 21216764 its reverse (46761212), we get a palindrome (67977976).

The spelling of 21216764 in words is "twenty-one million, two hundred sixteen thousand, seven hundred sixty-four".