21205025 has 6 divisors (see below), whose sum is σ = 26294262. Its totient is φ = 16964000.

The previous prime is 21205021. The next prime is 21205027. The reversal of 21205025 is 52050212.

It can be written as a sum of positive squares in 3 ways, for example, as 3598609 + 17606416 = 1897^2 + 4196^2 .

It is not a de Polignac number, because 21205025 - 2² = 21205021 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21204994 and 21205012.

It is not an unprimeable number, because it can be changed into a prime (21205021) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 424076 + ... + 424125.

It is an arithmetic number, because the mean of its divisors is an integer number (4382377).

Almost surely, 2^21205025 is an apocalyptic number.

21205025 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21205025 is a deficient number, since it is larger than the sum of its proper divisors (5089237).

21205025 is an equidigital number, since it uses as much as digits as its factorization.

21205025 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 848211 (or 848206 counting only the distinct ones).

The product of its (nonzero) digits is 200, while the sum is 17.

The square root of 21205025 is about 4604.8914210869. The cubic root of 21205025 is about 276.7873660870.

Adding to 21205025 its reverse (52050212), we get a palindrome (73255237).

The spelling of 21205025 in words is "twenty-one million, two hundred five thousand, twenty-five".