21125128 has 16 divisors (see below), whose sum is σ = 39756780. Its totient is φ = 10523328.

The previous prime is 21125123. The next prime is 21125161. The reversal of 21125128 is 82152112.

It can be written as a sum of positive squares in 2 ways, for example, as 18507204 + 2617924 = 4302^2 + 1618^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21125099 and 21125108.

It is not an unprimeable number, because it can be changed into a prime (21125123) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2551 + ... + 6982.

Almost surely, 2^21125128 is an apocalyptic number.

It is an amenable number.

21125128 is a deficient number, since it is larger than the sum of its proper divisors (18631652).

21125128 is a wasteful number, since it uses less digits than its factorization.

21125128 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9816 (or 9812 counting only the distinct ones).

The product of its digits is 320, while the sum is 22.

The square root of 21125128 is about 4596.2080022558. The cubic root of 21125128 is about 276.4392990127.

The spelling of 21125128 in words is "twenty-one million, one hundred twenty-five thousand, one hundred twenty-eight".