21821644 has 24 divisors (see below), whose sum is σ = 42455168. Its totient is φ = 9745920.

The previous prime is 21821629. The next prime is 21821647. The reversal of 21821644 is 44612812.

It is not an unprimeable number, because it can be changed into a prime (21821647) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5157 + ... + 8380.

Almost surely, 2^21821644 is an apocalyptic number.

It is an amenable number.

21821644 is a deficient number, since it is larger than the sum of its proper divisors (20633524).

21821644 is a wasteful number, since it uses less digits than its factorization.

21821644 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13585 (or 13583 counting only the distinct ones).

The product of its digits is 3072, while the sum is 28.

The square root of 21821644 is about 4671.3642546905. The cubic root of 21821644 is about 279.4446646150. Note that the first 3 decimals are identical.

The spelling of 21821644 in words is "twenty-one million, eight hundred twenty-one thousand, six hundred forty-four".