21205171 has 16 divisors (see below), whose sum is σ = 24343200. Its totient is φ = 18298368.

The previous prime is 21205169. The next prime is 21205183. The reversal of 21205171 is 17150212.

It is a cyclic number.

It is not a de Polignac number, because 21205171 - 2¹ = 21205169 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21205111) 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 15 ways as a sum of consecutive naturals, for example, 50400 + ... + 50818.

It is an arithmetic number, because the mean of its divisors is an integer number (1521450).

Almost surely, 2^21205171 is an apocalyptic number.

21205171 is a deficient number, since it is larger than the sum of its proper divisors (3138029).

21205171 is a wasteful number, since it uses less digits than its factorization.

21205171 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 678.

The product of its (nonzero) digits is 140, while the sum is 19.

The square root of 21205171 is about 4604.9072737678. The cubic root of 21205171 is about 276.7880013273.

Adding to 21205171 its reverse (17150212), we get a palindrome (38355383).

The spelling of 21205171 in words is "twenty-one million, two hundred five thousand, one hundred seventy-one".