21684289 has 6 divisors (see below), whose sum is σ = 23834930. Its totient is φ = 19712880.

The previous prime is 21684287. The next prime is 21684293. The reversal of 21684289 is 98248612.

It can be written as a sum of positive squares in only one way, i.e., 21344400 + 339889 = 4620^2 + 583^2 .

It is not a de Polignac number, because 21684289 - 2¹ = 21684287 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21684287) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 89484 + ... + 89725.

Almost surely, 2^21684289 is an apocalyptic number.

It is an amenable number.

21684289 is a deficient number, since it is larger than the sum of its proper divisors (2150641).

21684289 is a wasteful number, since it uses less digits than its factorization.

21684289 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 179231 (or 179220 counting only the distinct ones).

The product of its digits is 55296, while the sum is 40.

The square root of 21684289 is about 4656.6392387644. The cubic root of 21684289 is about 278.8571143505.

The spelling of 21684289 in words is "twenty-one million, six hundred eighty-four thousand, two hundred eighty-nine".