21521525 has 6 divisors (see below), whose sum is σ = 26686722. Its totient is φ = 17217200.

The previous prime is 21521503. The next prime is 21521527. The reversal of 21521525 is 52512512.

It can be written as a sum of positive squares in 3 ways, for example, as 4024036 + 17497489 = 2006^2 + 4183^2 .

It is not a de Polignac number, because 21521525 - 2¹² = 21517429 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21521525.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21521527) 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 5 ways as a sum of consecutive naturals, for example, 430406 + ... + 430455.

It is an arithmetic number, because the mean of its divisors is an integer number (4447787).

Almost surely, 2^21521525 is an apocalyptic number.

21521525 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21521525 is a deficient number, since it is larger than the sum of its proper divisors (5165197).

21521525 is an equidigital number, since it uses as much as digits as its factorization.

21521525 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 860871 (or 860866 counting only the distinct ones).

The product of its digits is 1000, while the sum is 23.

The square root of 21521525 is about 4639.1297675318. The cubic root of 21521525 is about 278.1576534485.

The spelling of 21521525 in words is "twenty-one million, five hundred twenty-one thousand, five hundred twenty-five".