21644418 has 16 divisors (see below), whose sum is σ = 43334496. Its totient is φ = 7207200.

The previous prime is 21644407. The next prime is 21644419. The reversal of 21644418 is 81444612.

It is not an unprimeable number, because it can be changed into a prime (21644419) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9805 + ... + 11807.

It is an arithmetic number, because the mean of its divisors is an integer number (2708406).

Almost surely, 2^21644418 is an apocalyptic number.

21644418 is an abundant number, since it is smaller than the sum of its proper divisors (21690078).

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

21644418 is a wasteful number, since it uses less digits than its factorization.

21644418 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3809.

The product of its digits is 6144, while the sum is 30.

The square root of 21644418 is about 4652.3561772504. The cubic root of 21644418 is about 278.6860975465.

The spelling of 21644418 in words is "twenty-one million, six hundred forty-four thousand, four hundred eighteen".