21684851 has 2 divisors, whose sum is σ = 21684852. Its totient is φ = 21684850.

The previous prime is 21684827. The next prime is 21684853. The reversal of 21684851 is 15848612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21684851 - 2¹⁸ = 21422707 is a prime.

Together with 21684853, 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 (21684853) 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, 10842425 + 10842426.

It is an arithmetic number, because the mean of its divisors is an integer number (10842426).

Almost surely, 2^21684851 is an apocalyptic number.

21684851 is a deficient number, since it is larger than the sum of its proper divisors (1).

21684851 is an equidigital number, since it uses as much as digits as its factorization.

21684851 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 15360, while the sum is 35.

The square root of 21684851 is about 4656.6995823222. The cubic root of 21684851 is about 278.8595234118.

The spelling of 21684851 in words is "twenty-one million, six hundred eighty-four thousand, eight hundred fifty-one".