21684659 has 2 divisors, whose sum is σ = 21684660. Its totient is φ = 21684658.

The previous prime is 21684647. The next prime is 21684661. The reversal of 21684659 is 95648612.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21684659 is a prime.

It is a super-4 number, since 4×21684659⁴ (a number of 30 digits) contains 4444 as substring.

Together with 21684661, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21684679) 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 as a sum of consecutive naturals, namely, 10842329 + 10842330.

It is an arithmetic number, because the mean of its divisors is an integer number (10842330).

Almost surely, 2^21684659 is an apocalyptic number.

21684659 is a deficient number, since it is larger than the sum of its proper divisors (1).

21684659 is an equidigital number, since it uses as much as digits as its factorization.

21684659 is an odious number, because the sum of its binary digits is odd.

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

The square root of 21684659 is about 4656.6789668174. The cubic root of 21684659 is about 278.8587003920.

The spelling of 21684659 in words is "twenty-one million, six hundred eighty-four thousand, six hundred fifty-nine".