21505125 has 16 divisors (see below), whose sum is σ = 35785152. Its totient is φ = 11469200.

The previous prime is 21505109. The next prime is 21505129. The reversal of 21505125 is 52150512.

It is not a de Polignac number, because 21505125 - 2⁴ = 21505109 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21505129) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 28299 + ... + 29048.

It is an arithmetic number, because the mean of its divisors is an integer number (2236572).

Almost surely, 2^21505125 is an apocalyptic number.

21505125 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21505125 is a deficient number, since it is larger than the sum of its proper divisors (14280027).

21505125 is an equidigital number, since it uses as much as digits as its factorization.

21505125 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 57365 (or 57355 counting only the distinct ones).

The product of its (nonzero) digits is 500, while the sum is 21.

The square root of 21505125 is about 4637.3618577808. The cubic root of 21505125 is about 278.0869808739.

Adding to 21505125 its reverse (52150512), we get a palindrome (73655637).

The spelling of 21505125 in words is "twenty-one million, five hundred five thousand, one hundred twenty-five".