21205275 has 72 divisors (see below), whose sum is σ = 43568640. Its totient is φ = 8910720.

The previous prime is 21205243. The next prime is 21205279. The reversal of 21205275 is 57250212.

It is not a de Polignac number, because 21205275 - 2⁵ = 21205243 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21205279) 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 71 ways as a sum of consecutive naturals, for example, 88606 + ... + 88844.

It is an arithmetic number, because the mean of its divisors is an integer number (605120).

Almost surely, 2^21205275 is an apocalyptic number.

21205275 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21205275 is an abundant number, since it is smaller than the sum of its proper divisors (22363365).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21205275 is a wasteful number, since it uses less digits than its factorization.

21205275 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 285 (or 267 counting only the distinct ones).

The product of its (nonzero) digits is 1400, while the sum is 24.

The square root of 21205275 is about 4604.9185660552. The cubic root of 21205275 is about 276.7884538255.

Adding to 21205275 its reverse (57250212), we get a palindrome (78455487).

The spelling of 21205275 in words is "twenty-one million, two hundred five thousand, two hundred seventy-five".