21508125 has 20 divisors (see below), whose sum is σ = 35838528. Its totient is φ = 11470000.

The previous prime is 21508121. The next prime is 21508153. The reversal of 21508125 is 52180512.

It is not a de Polignac number, because 21508125 - 2² = 21508121 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21508095 and 21508104.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21508121) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 3861 + ... + 7610.

Almost surely, 2^21508125 is an apocalyptic number.

21508125 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21508125 is a deficient number, since it is larger than the sum of its proper divisors (14330403).

21508125 is an equidigital number, since it uses as much as digits as its factorization.

21508125 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11494 (or 11479 counting only the distinct ones).

The product of its (nonzero) digits is 800, while the sum is 24.

The square root of 21508125 is about 4637.6853062708. The cubic root of 21508125 is about 278.0999114684.

Adding to 21508125 its reverse (52180512), we get a palindrome (73688637).

The spelling of 21508125 in words is "twenty-one million, five hundred eight thousand, one hundred twenty-five".