21687199 has 2 divisors, whose sum is σ = 21687200. Its totient is φ = 21687198.

The previous prime is 21687191. The next prime is 21687203. The reversal of 21687199 is 99178612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21687199 - 2³ = 21687191 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21687191) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10843599 + 10843600.

It is an arithmetic number, because the mean of its divisors is an integer number (10843600).

Almost surely, 2^21687199 is an apocalyptic number.

21687199 is a deficient number, since it is larger than the sum of its proper divisors (1).

21687199 is an equidigital number, since it uses as much as digits as its factorization.

21687199 is an evil number, because the sum of its binary digits is even.

The product of its digits is 54432, while the sum is 43.

The square root of 21687199 is about 4656.9516853839. The cubic root of 21687199 is about 278.8695878654.

The spelling of 21687199 in words is "twenty-one million, six hundred eighty-seven thousand, one hundred ninety-nine".