21819665 has 16 divisors (see below), whose sum is σ = 30237312. Its totient is φ = 14805504.

The previous prime is 21819659. The next prime is 21819673. The reversal of 21819665 is 56691812.

It is not a de Polignac number, because 21819665 - 2⁶ = 21819601 is a prime.

It is a Curzon number.

It is an unprimeable number.

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, 182 + ... + 6608.

It is an arithmetic number, because the mean of its divisors is an integer number (1889832).

Almost surely, 2^21819665 is an apocalyptic number.

It is an amenable number.

21819665 is a deficient number, since it is larger than the sum of its proper divisors (8417647).

21819665 is an equidigital number, since it uses as much as digits as its factorization.

21819665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6536.

The product of its digits is 25920, while the sum is 38.

The square root of 21819665 is about 4671.1524273995. The cubic root of 21819665 is about 279.4362167683.

The spelling of 21819665 in words is "twenty-one million, eight hundred nineteen thousand, six hundred sixty-five".