21644090 has 32 divisors (see below), whose sum is σ = 42166656. Its totient is φ = 7951680.

The previous prime is 21644089. The next prime is 21644099. The reversal of 21644090 is 9044612.

It is a Smith number, since the sum of its digits (26) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Harshad number since it is a multiple of its sum of digits (26).

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21644099) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 42779 + ... + 43281.

It is an arithmetic number, because the mean of its divisors is an integer number (1317708).

Almost surely, 2^21644090 is an apocalyptic number.

21644090 is a deficient number, since it is larger than the sum of its proper divisors (20522566).

21644090 is a wasteful number, since it uses less digits than its factorization.

21644090 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 854.

The product of its (nonzero) digits is 1728, while the sum is 26.

The square root of 21644090 is about 4652.3209261615. The cubic root of 21644090 is about 278.6846898009.

The spelling of 21644090 in words is "twenty-one million, six hundred forty-four thousand, ninety".