21128425 has 6 divisors (see below), whose sum is σ = 26199278. Its totient is φ = 16902720.

The previous prime is 21128411. The next prime is 21128441. The reversal of 21128425 is 52482112.

It can be written as a sum of positive squares in 3 ways, for example, as 7080921 + 14047504 = 2661^2 + 3748^2 .

It is not a de Polignac number, because 21128425 - 2⁹ = 21127913 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (25), and also a Moran number because the ratio is a prime number: 845137 = 21128425 / (2 + 1 + 1 + 2 + 8 + 4 + 2 + 5).

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 21128425.

It is an unprimeable number.

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, 422544 + ... + 422593.

Almost surely, 2^21128425 is an apocalyptic number.

21128425 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21128425 is a deficient number, since it is larger than the sum of its proper divisors (5070853).

21128425 is an equidigital number, since it uses as much as digits as its factorization.

21128425 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 845147 (or 845142 counting only the distinct ones).

The product of its digits is 1280, while the sum is 25.

The square root of 21128425 is about 4596.5666534926. The cubic root of 21128425 is about 276.4536795640.

The spelling of 21128425 in words is "twenty-one million, one hundred twenty-eight thousand, four hundred twenty-five".