21684689 has 4 divisors (see below), whose sum is σ = 23352756. Its totient is φ = 20016624.

The previous prime is 21684679. The next prime is 21684713. The reversal of 21684689 is 98648612.

It is a happy number.

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 11444689 + 10240000 = 3383^2 + 3200^2 .

It is a cyclic number.

It is not a de Polignac number, because 21684689 - 2²⁴ = 4907473 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21684659) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 834014 + ... + 834039.

It is an arithmetic number, because the mean of its divisors is an integer number (5838189).

Almost surely, 2^21684689 is an apocalyptic number.

It is an amenable number.

21684689 is a deficient number, since it is larger than the sum of its proper divisors (1668067).

21684689 is a wasteful number, since it uses less digits than its factorization.

21684689 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1668066.

The product of its digits is 165888, while the sum is 44.

The square root of 21684689 is about 4656.6821879961. The cubic root of 21684689 is about 278.8588289891.

The spelling of 21684689 in words is "twenty-one million, six hundred eighty-four thousand, six hundred eighty-nine".