21684679 has 2 divisors, whose sum is σ = 21684680. Its totient is φ = 21684678.

The previous prime is 21684661. The next prime is 21684713. The reversal of 21684679 is 97648612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21684679 - 2⁵ = 21684647 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21684659) 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, 10842339 + 10842340.

It is an arithmetic number, because the mean of its divisors is an integer number (10842340).

Almost surely, 2^21684679 is an apocalyptic number.

21684679 is a deficient number, since it is larger than the sum of its proper divisors (1).

21684679 is an equidigital number, since it uses as much as digits as its factorization.

21684679 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 145152, while the sum is 43.

The square root of 21684679 is about 4656.6811142701. The cubic root of 21684679 is about 278.8587861234.

The spelling of 21684679 in words is "twenty-one million, six hundred eighty-four thousand, six hundred seventy-nine".