21678659 has 2 divisors, whose sum is σ = 21678660. Its totient is φ = 21678658.

The previous prime is 21678623. The next prime is 21678661. The reversal of 21678659 is 95687612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21678659 - 2²⁰ = 20630083 is a prime.

It is a Sophie Germain prime.

Together with 21678661, 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 (21678959) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10839329 + 10839330.

It is an arithmetic number, because the mean of its divisors is an integer number (10839330).

Almost surely, 2^21678659 is an apocalyptic number.

21678659 is a deficient number, since it is larger than the sum of its proper divisors (1).

21678659 is an equidigital number, since it uses as much as digits as its factorization.

21678659 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 181440, while the sum is 44.

The square root of 21678659 is about 4656.0346862969. The cubic root of 21678659 is about 278.8329785742.

The spelling of 21678659 in words is "twenty-one million, six hundred seventy-eight thousand, six hundred fifty-nine".