21205979 has 12 divisors (see below), whose sum is σ = 22244040. Its totient is φ = 20203200.

The previous prime is 21205973. The next prime is 21205981. The reversal of 21205979 is 97950212.

It is a de Polignac number, because none of the positive numbers 2^k-21205979 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21205973) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 152492 + ... + 152630.

It is an arithmetic number, because the mean of its divisors is an integer number (1853670).

Almost surely, 2^21205979 is an apocalyptic number.

21205979 is a deficient number, since it is larger than the sum of its proper divisors (1038061).

21205979 is an equidigital number, since it uses as much as digits as its factorization.

21205979 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 302 (or 241 counting only the distinct ones).

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

The square root of 21205979 is about 4604.9950054262. The cubic root of 21205979 is about 276.7915168513.

The spelling of 21205979 in words is "twenty-one million, two hundred five thousand, nine hundred seventy-nine".