21646665 has 24 divisors (see below), whose sum is σ = 38537928. Its totient is φ = 11232000.

The previous prime is 21646633. The next prime is 21646721. The reversal of 21646665 is 56664612.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 962361 + 20684304 = 981^2 + 4548^2 .

It is not a de Polignac number, because 21646665 - 2⁵ = 21646633 is a prime.

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 23 ways as a sum of consecutive naturals, for example, 4836 + ... + 8165.

It is an arithmetic number, because the mean of its divisors is an integer number (1605747).

Almost surely, 2^21646665 is an apocalyptic number.

It is an amenable number.

21646665 is a deficient number, since it is larger than the sum of its proper divisors (16891263).

21646665 is a wasteful number, since it uses less digits than its factorization.

21646665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13049 (or 13046 counting only the distinct ones).

The product of its digits is 51840, while the sum is 36.

The square root of 21646665 is about 4652.5976615220. The cubic root of 21646665 is about 278.6957410797.

The spelling of 21646665 in words is "twenty-one million, six hundred forty-six thousand, six hundred sixty-five".