21644764 has 12 divisors (see below), whose sum is σ = 37918888. Its totient is φ = 10810800.

The previous prime is 21644747. The next prime is 21644801. The reversal of 21644764 is 46744612.

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, 2374 + ... + 6994.

Almost surely, 2^21644764 is an apocalyptic number.

It is an amenable number.

21644764 is a deficient number, since it is larger than the sum of its proper divisors (16274124).

21644764 is a wasteful number, since it uses less digits than its factorization.

21644764 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5796 (or 5794 counting only the distinct ones).

The product of its digits is 32256, while the sum is 34.

The square root of 21644764 is about 4652.3933625608. The cubic root of 21644764 is about 278.6875825310.

The spelling of 21644764 in words is "twenty-one million, six hundred forty-four thousand, seven hundred sixty-four".