21668019 has 4 divisors (see below), whose sum is σ = 28890696. Its totient is φ = 14445344.

The previous prime is 21668011. The next prime is 21668033. The reversal of 21668019 is 91086612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21668019 - 2³ = 21668011 is a prime.

It is a super-2 number, since 2×21668019² = 939006094768722, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21668011) 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 in 3 ways as a sum of consecutive naturals, for example, 3611334 + ... + 3611339.

It is an arithmetic number, because the mean of its divisors is an integer number (7222674).

Almost surely, 2^21668019 is an apocalyptic number.

21668019 is a deficient number, since it is larger than the sum of its proper divisors (7222677).

21668019 is an equidigital number, since it uses as much as digits as its factorization.

21668019 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7222676.

The product of its (nonzero) digits is 5184, while the sum is 33.

The square root of 21668019 is about 4654.8919428919. The cubic root of 21668019 is about 278.7873535443.

The spelling of 21668019 in words is "twenty-one million, six hundred sixty-eight thousand, nineteen".