21684569 has 4 divisors (see below), whose sum is σ = 21883620. Its totient is φ = 21485520.

The previous prime is 21684557. The next prime is 21684589. The reversal of 21684569 is 96548612.

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 19758025 + 1926544 = 4445^2 + 1388^2 .

It is a cyclic number.

It is not a de Polignac number, because 21684569 - 2¹² = 21680473 is a prime.

It is a super-2 number, since 2×21684569² = 940441065431522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21684589) 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, 99362 + ... + 99579.

It is an arithmetic number, because the mean of its divisors is an integer number (5470905).

Almost surely, 2^21684569 is an apocalyptic number.

It is an amenable number.

21684569 is a deficient number, since it is larger than the sum of its proper divisors (199051).

21684569 is a wasteful number, since it uses less digits than its factorization.

21684569 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 199050.

The product of its digits is 103680, while the sum is 41.

The square root of 21684569 is about 4656.6693032682. The cubic root of 21684569 is about 278.8583145997.

The spelling of 21684569 in words is "twenty-one million, six hundred eighty-four thousand, five hundred sixty-nine".