21644065 has 4 divisors (see below), whose sum is σ = 25972884. Its totient is φ = 17315248.

The previous prime is 21644053. The next prime is 21644089. The reversal of 21644065 is 56044612.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 16257024 + 5387041 = 4032^2 + 2321^2 .

It is a cyclic number.

It is not a de Polignac number, because 21644065 - 2⁵ = 21644033 is a prime.

It is a Duffinian 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, 2164402 + ... + 2164411.

It is an arithmetic number, because the mean of its divisors is an integer number (6493221).

Almost surely, 2^21644065 is an apocalyptic number.

It is an amenable number.

21644065 is a deficient number, since it is larger than the sum of its proper divisors (4328819).

21644065 is an equidigital number, since it uses as much as digits as its factorization.

21644065 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4328818.

The product of its (nonzero) digits is 5760, while the sum is 28.

The square root of 21644065 is about 4652.3182393297. The cubic root of 21644065 is about 278.6845825026.

Adding to 21644065 its reverse (56044612), we get a palindrome (77688677).

The spelling of 21644065 in words is "twenty-one million, six hundred forty-four thousand, sixty-five".