21684665 has 8 divisors (see below), whose sum is σ = 26052360. Its totient is φ = 17327232.

The previous prime is 21684661. The next prime is 21684679. The reversal of 21684665 is 56648612.

It can be written as a sum of positive squares in 4 ways, for example, as 2042041 + 19642624 = 1429^2 + 4432^2 .

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 21684665 - 2² = 21684661 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21684661) by changing a digit.

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, 3317 + ... + 7373.

It is an arithmetic number, because the mean of its divisors is an integer number (3256545).

Almost surely, 2^21684665 is an apocalyptic number.

It is an amenable number.

21684665 is a deficient number, since it is larger than the sum of its proper divisors (4367695).

21684665 is a wasteful number, since it uses less digits than its factorization.

21684665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5131.

The product of its digits is 69120, while the sum is 38.

The square root of 21684665 is about 4656.6796110534. The cubic root of 21684665 is about 278.8587261114.

The spelling of 21684665 in words is "twenty-one million, six hundred eighty-four thousand, six hundred sixty-five".