21205799 has 4 divisors (see below), whose sum is σ = 21249480. Its totient is φ = 21162120.

The previous prime is 21205781. The next prime is 21205801. The reversal of 21205799 is 99750212.

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 21205799 - 2⁸ = 21205543 is a prime.

It is a super-2 number, since 2×21205799² = 899371822456802, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21205759) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 21104 + ... + 22085.

It is an arithmetic number, because the mean of its divisors is an integer number (5312370).

Almost surely, 2^21205799 is an apocalyptic number.

21205799 is a deficient number, since it is larger than the sum of its proper divisors (43681).

21205799 is an equidigital number, since it uses as much as digits as its factorization.

21205799 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 43680.

The product of its (nonzero) digits is 11340, while the sum is 35.

The square root of 21205799 is about 4604.9754613896. The cubic root of 21205799 is about 276.7907336978.

The spelling of 21205799 in words is "twenty-one million, two hundred five thousand, seven hundred ninety-nine".