21665705 has 8 divisors (see below), whose sum is σ = 26070792. Its totient is φ = 17284608.

The previous prime is 21665689. The next prime is 21665713. The reversal of 21665705 is 50756612.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 1478656 + 20187049 = 1216^2 + 4493^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21665705 - 2⁴ = 21665689 is a prime.

It is a Duffinian number.

It is an unprimeable number.

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, 3944 + ... + 7673.

It is an arithmetic number, because the mean of its divisors is an integer number (3258849).

Almost surely, 2^21665705 is an apocalyptic number.

It is an amenable number.

21665705 is a deficient number, since it is larger than the sum of its proper divisors (4405087).

21665705 is a wasteful number, since it uses less digits than its factorization.

21665705 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11995.

The product of its (nonzero) digits is 12600, while the sum is 32.

The square root of 21665705 is about 4654.6433805395. The cubic root of 21665705 is about 278.7774289806. Note that the first 3 decimals are identical.

The spelling of 21665705 in words is "twenty-one million, six hundred sixty-five thousand, seven hundred five".