21666199 has 4 divisors (see below), whose sum is σ = 21675600. Its totient is φ = 21656800.

The previous prime is 21666191. The next prime is 21666209. The reversal of 21666199 is 99166612.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21666199 - 2³ = 21666191 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21666191) 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 in 3 ways as a sum of consecutive naturals, for example, 1374 + ... + 6724.

It is an arithmetic number, because the mean of its divisors is an integer number (5418900).

Almost surely, 2^21666199 is an apocalyptic number.

21666199 is a deficient number, since it is larger than the sum of its proper divisors (9401).

21666199 is an equidigital number, since it uses as much as digits as its factorization.

21666199 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9400.

The product of its digits is 34992, while the sum is 40.

The square root of 21666199 is about 4654.6964455268. The cubic root of 21666199 is about 278.7795477670.

The spelling of 21666199 in words is "twenty-one million, six hundred sixty-six thousand, one hundred ninety-nine".