21205725 has 24 divisors (see below), whose sum is σ = 35206080. Its totient is φ = 11262720.

The previous prime is 21205703. The next prime is 21205727. The reversal of 21205725 is 52750212.

It is not a de Polignac number, because 21205725 - 2⁶ = 21205661 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21205695 and 21205704.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21205727) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 24856 + ... + 25694.

It is an arithmetic number, because the mean of its divisors is an integer number (1466920).

Almost surely, 2^21205725 is an apocalyptic number.

21205725 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21205725 is a deficient number, since it is larger than the sum of its proper divisors (14000355).

21205725 is a wasteful number, since it uses less digits than its factorization.

21205725 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1189 (or 1184 counting only the distinct ones).

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

The square root of 21205725 is about 4604.9674265949. The cubic root of 21205725 is about 276.7904117334.

Adding to 21205725 its reverse (52750212), we get a palindrome (73955937).

The spelling of 21205725 in words is "twenty-one million, two hundred five thousand, seven hundred twenty-five".