21525021 has 20 divisors (see below), whose sum is σ = 36749152. Its totient is φ = 12299688.

The previous prime is 21525017. The next prime is 21525059. The reversal of 21525021 is 12052512.

It is not a de Polignac number, because 21525021 - 2² = 21525017 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21524985 and 21525003.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21525001) 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 19 ways as a sum of consecutive naturals, for example, 18415 + ... + 19548.

Almost surely, 2^21525021 is an apocalyptic number.

21525021 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21525021 is a deficient number, since it is larger than the sum of its proper divisors (15224131).

21525021 is an equidigital number, since it uses as much as digits as its factorization.

21525021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 37982 (or 37973 counting only the distinct ones).

The product of its (nonzero) digits is 200, while the sum is 18.

The square root of 21525021 is about 4639.5065470371. The cubic root of 21525021 is about 278.1727141301.

Adding to 21525021 its reverse (12052512), we get a palindrome (33577533).

The spelling of 21525021 in words is "twenty-one million, five hundred twenty-five thousand, twenty-one".